If you have a robust warranty just do it.. such an amazing car that has to be owned at least once. It still looks the business, is extremely comfortable, and when I saw a red CL55 on the motorway yesterday I was transfixed
But costs.. OMG.. just have a look how much the basic items will cost you..
Coil pack. a grand!
Cup holder.. 100 quid.
Set of (24) spark plugs for 500 quid I believe.
1 injector, 200 quid
there are just so many things to go wrong, such as the vacuum locks on the doors and boot, the 14 position heated and cooled massage seats.. the car is so complex.
luckily I didn't get into brakes, ABC failures and other items int he 2 months I had the car.. but as I had no warranty I wasn't about to spend all my spare cash on keeping this on the road.
There is a lot of info on these though including how-to's and DIY guides, if you are so inclined it would save you a lot. For example I was reading on Mbworld how to repair the door closing vacuum lock with some adhesive rather than paying 600 quid for a new lock.. because these will go.
Plus if you tune the CL600 it will match the power of the CL65 (which they only made 200 of in 2005/6, btw)
Just to add that I didnt get the chance to make the most out of the COMAND side of things as my Japanese version wasn't compatible in many ways, but you should be able to fit a bluetooth adaptor, have Video in Motion activated, and a few other tricks which are nice to do. It was still a joy to drive though and I have never felt such power, you are literally pinned to the back of your seat under acceleration. I would have kept the car If I had had a warranty or could have afforded to keep it as a garage queen for occasional use. But these days I cant justify that (wife, kid and mortgage comes first) and have no place to work on a car as I like in an apartment block.
I know I wont get a second chance to own as the 65 is so rare, but I am pleased to have had the privilege.
good luck and enjoy, if you choose to go for it