i've only owned my 93 s600 coupe for a year now but have had huge fun with it. have driven about 6000miles in total and it hasn't missed a beat for me in that time despite having some long standing issues that i have only just recently had funds to address.
ADS light on from purchase - body acceleration sensor at fault
left rear shock absorber failed lower bush
steering items failed: tracking out as well
all of the above cost £2354 through dealership, £670 for labour the rest was for parts only.
it's important to stress that the above items did not stop the vehicle working however it was just a tank that kept rolling.
the main problems itemised above were due to the car have been left sitting outside for over 2years before my purchase.
other issues that i fixed myself for minimal cost:
door check arm sheared (just welded the parts back on)
radio antenna failed (easy to fix)
door soft close vaccum sender (split casing)
sun roof not opening closing easy (just needed lube)
washer nozzles blocked
websites of great assistance to me:
this website and forum is awesome and there are some great people on here with outstanding knowledge.
V12 Uber Alles, Articles and Info Page
K6JRF Auto Page
these are phenomenal cars and i have not regretted my purchase, the car cost me £3000 and had 117K miles on it.
hope this helps and good luck. if you want anymore info let me know. i'm still learning stuff and there are many more that have superior knowledge on this forum but i'll gladly share more with you if it helps.