I have a 2005 SL500 with 85,000 km. A few days ago it would not start right away. Second try it started but ran terrible. Check engine light came on but went out again. This is the weird part, my car started to raise and lower with all the interior dash warning lights going on and off. I also had a knock coming from the drivers side and was loud at the rear of the car. I took it to the dealer Three Point Motors in Victoria BC. The dealership found that someone had placed a rock into my exhaust which caused the loud knock. With the starting problem the Crank position sensor was replaced and now the car idles smooth and all problems are gone. The lights on the dash do not go on and off anymore. The repair would have cost $300 but they waived all charges since I purchased the car there with a minimal warranty on the engine four months ago.

I remember just after I bought the car all of the dash lights went on and off on my dash just like this time. It was my trunk battery. After replacing the battery all problems resolved.

I think if you have a good dealership then you might save replacing everything just to find the problem. When I purchased the car I thought I would replace the trans fluid and called around to other dealerships. They said sure we will do it for $600. When I called Three Point Motors the first thing they said was that my car only has 85,000 km on it and the trans service is due at 133,000 km. Save your money till then. Seems like an honest dealership to me. I live outside Vancouver BC and I take a ferry to the island and stay over night to get my car serviced. Finding a good honest dealership is hard and I think I found a good one. Some items might be too expensive so I will take it as the problems arise. I hope this information can help someone else with a similar problem.
Have a great day.