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Discussion Starter #1
Hi everyone:
I have a 1998 SLK 230 since new. Today I decided on changing the cabin air filter for the first time in 20 years. Thought it was about due. Anyway, when I took of the yellow clips that hold the filter cover on, I droped on on the back of the footrest. I removed the rug, a foam piece behind the rug a felt the foam on the floor was soakes with what I can describe as some sort of oily yellowish substance. Any idea what this “oil” can be? Thanks for the help.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Sounds like hydraulic fluid from your front roof cylinders
 

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Discussion Starter #3
If that’s what it is, then it’s not a problem. I changed all cyclinders and pump about 7 years ago when the stopped working. They are working fine now so all I have to do is clean it. Hiw did it get there? Dropped down the A pillar? There doesn’t seem to be any part full of oil around there so I hope that’s what it is. Thanks a lot for the extremely prompt reply.
 

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Super Moderator UK 2002 SLK320 Blue
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Let's be careful here.... It could be ATF from the gearbox.

Take the carpet out, take the white foam board out, undo the three nylon bolts on the metal plate and lower the plate to the footwell floor. You should have a bundle of wires connecting to a module on the metal plate. That's your TCU - Transmission control module.

If the loom is sticky with this fluid then the O-rings in your pilot bushing in the gearbox have failed and ATF is wicking up the loom to the TCU. Then it's time to change your ATF, filter, gasket and pilot bushing.

I'll see if I can find a photo of mine and show you.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Administrator 2009 SLK 55 AMG/Founding Member 2006
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See? I send for experts and one shows up1 :D
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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Is ATF fluid yellow? Thought it was 'reddish'
 

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Super Moderator UK 2002 SLK320 Blue
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Discussion Starter #10
That picture sure looks like my car. I did rebuilt the transmission at 82k but that was in 2011. So, if it’s ATF fluid, can I measure the ATF and see that it’s low? The yellow color vould be due to the yellow foam in the floor of the car. I suppose doing this change is not a DIY job, is it? Thanks again for the help.
 

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Super Moderator UK 2002 SLK320 Blue
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It's possible as a DIY but much, much easier on a lift. Plus you can get at everything from underneath. The pilot bushing is a bear if you can't get your fingers in. See picture.

If you've changed the fluid before then you should have a dipstick. Try measuring it again with that. Did you change the bushing when you changed the fluid and filter?
 

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Discussion Starter #12
I serviced the whole transmission, not only the oil but I don’t believe I have the dipstick. Mechanic installed a new plug but similar to the original one. I guess it’s better just to buy the parts fo the job. Even if that’s not the cause, which I do believe it is, it never hurts to change the ATF. It’s been there for 7 years. Our weather here is hot and humid and the traffic around town is stop and go so transmissions fo get a workout. Again, thanks for your time.
 

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Premium Member 1999 SLK 5.4 M113
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I think earlier ATF fluids were brownish.. which could appear yellow next to the yellow foam or on a white surface.

I can tell you for sure that the original fluid in my SLK was light brown.
 

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Discussion Starter #14
This oil is definitely yellow or gold color. I suppose I can compare it to the transmission oil by getting some from the transmision through the hole to check level. There seems to be a larger amount than what I could expect to wick through the loom but then again, who knows how long this has been going on.
 

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Super Moderator UK 2002 SLK320 Blue
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What’s that black corrugated tube in the first picture? My car also has that but I have no idea what it is for.
It helps ventilate the area and keep the equipment there cool.
 

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Discussion Starter #18
I checked the color of the transmission oil and it definitely is clear red and looks and smells fresh, or at least what I think fresh transmission oil smells like. I’m not a transmission oil conosseur. Tomorrow I’ll buy the measuring tool to check the level. The engine oil is golden yellow, similar to what I found in the well. The level however is on the high mark. Does seem to have lost any, at least since the last oil change. The saga continues.
 

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Discussion Starter #19
This morning I got the measuring tool, $60.00 but my supplier said just to use it and return it. To expensive for once a year use. Nice of him. The level was perfect. Color clear red and looks fresh. I had the whole transmission rebuilt 20k miles ago so maybe this oil is from that time. Looked at the wire loom from the botton and it looks good. No apparent leaks. Rug is looks brand new so whatever leaked here, had to come from behind the rug. No appreciable oil track fron A pillar so it seems it was not the roof cylinder. I’ll just keep an eye on the transmission fluid. This oil must have beennthere a long time, since last rebuilt. Thank you all for your help. If I find somethind else, I’ll let you know but I’m convinced that’s what happened.
 

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Super Moderator UK 2002 SLK320 Blue
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Maybe it's the leftovers from before the previous ATF change. Either way, you'd do well to clean off what you can with electrical contact cleaner on the loom and in the TCU's connectors, just in case any has penetrated the TCU. Maybe the ATF chabnges colour when exposed to copper wires? I don't know.
 
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