I considered getting an SL instead of my SLK a year ago.
I ended going SLK because I could get a proper gearbox as opposed to an auto. However, when I inevitably have to sell my car when I move to the USA I will probably go the SL route. I got to drive a SL65 for a week while my SLK350 was coming up from the US and I loved it. Power aside - it was comfortable, well equipped, and actually not too terrible on petrol. The manual gearbox was the differentiating factor for me at the time. Now... I am not so sure.
During my buying process I turned out two major points one should look for when considering purchasing an SL.
1) Look at the cars maintenance history. If it has the ABC suspension were the struts ever replaced or was it system itself ever serviced? Getting an ABC strut replaced is $1200 per corner and is the most common issue on R230s. There are ways you can test the health of the system sans-tool, I cannot remember them but they are very simple and are mostly observational, can be done without alerting a salesman.
2) The rear glass roof panel (heated window) seal tends to shrink where it is supposed to seal with the trunk. Even if the car has lived in a garage it's whole life it can suffer from this as hot temperatures will cause the shrinking, but UV exposure accelerates it. The cost to replace the seal is ~$700, and if it is not replaced water can go into the trunk when it rains.
Features you WANT (that are surprisingly optional):
- Keyless GO - You can tell this is present in a SL if there is a button on the top of the shifter (says Start/Stop), if you can;t see in pictures clearly look for a chrome ring with a circle depression in it. If it looks solid matte silver then it does not have it.
- Panoramic Roof (Sun roof) - you can tell by pictures if a SL has this (if it is not black) if the ceiling section of the roof is black on the exterior.
Both of these are MAJOR factors in functionality and desirability of the car when it comes time to sell down the road (if that is a concern). If a $15000 Nissan comes with a push to start button a six figure Mercedes should as well.
I would advise going for a mint 2003-2004, you get the 5G transmission when it reached it's final iteration (in non-AMG form). The engine and transmission in those are usually bullet proof, just the electronics to worry about.
SLs are lovely and I would happily own one - but if you do not get it thoroughly checked prior to sale you can run up four digit and even five digit repair bills very quickly.
Perfect example of a desirable SL - the exterior colour is the only problem, but it has everything.