Had an SLK with a slow roof problem last year. Eventually got really brave, stripped the unit down washed all the valves, pump and passageways down with brake cleaner reassembled and filled with new oil and it worked a treat. I am pretty sure that a fragment of swarf was trapped in a pressure relief valve and allowing all the hydraulic pressure to bleed off. Perhaps you have a similar problem. In the final analysis it wasn't rocket science but I always find it a bit daunting stripping something I've never been inside of before, especially as the manufacturer doesn't really want you to open it up anyway and wants a fortune for a new one. Shaun