Gorhad,
As far as I can remember I took the cylinder off with the roof up and locked into position.
My Advice:
- Take a lot of pictures of the assembly before you start taking screws out. There will be paint showing the position of things, and you want to be able to put it back exactly as it was when it came apart.
- The O kit ring will have lots of instructions. They are very beneficial.
- You can't disconnect the hydraulic lines from the cylinder. They are an integral unit. Therefore you will need to drill and work on the cylinder while the hydraulic lines are still attached to the car. I detached everything as far as possible and was able to get the cylinder outside of the car to work on it. A portable workbench with a vise would be a great help. I didn't have one. On a related note you want to free up the lines to get as much travel to work as possible. Thus you will be disconnecting the feed and return line as far back along the roof as you can. I believe that they ran down the RH side of the roof. Once again, take pics so that you know how it all goes back together.
- Be very careful when working with the cylinder. The last thing you want to do is to either get dirt or metal shavings in the system or to scratch the piston. Flushing the cylinder out with a solvent and wrapping the piston with electrical tape are both excellent strategies. The hardest part for me was actually getting the retaining ring back into position. If I had it to do over again I would do what another user did and use a snap ring of the same size and snap ring pliers instead.
- Try and lose as little hydraulic fluid as you can. The system is self bleeding (doesn't matter if you get air into the line) and has a reservoir attached to the pump. I didn't even have to add any extra hydraulic fluid after the repair. If you do then the pump is behind the seat and there's a thread on here on how to get to it.
Here's the best picture on what you are getting ready to do with the cylinder, courtesy of SLKWorld member Sokoloff.
SLK Top Cylinder Rebuild Guide with Cut-Away Diagrams - Mercedes-Benz Forum
Best Wishes,