Vintage Cars: 91 420SEL piston rings, piston rings, old gals

Question
Hi Ron,
I see that you specify knowledge with w126 up to 1985, however, I was wondering if you might be able to shed some light on my 1991 420SEL.
I just bought it for a couple hundred bucks for parts. The previous owner says he thinks there are 2 "dead" or damaged cylinders: lots of smoke from tailpipe and car shuts off after a few minutes. I'd like to open her up as I think its most likely damaged piston rings. My local mechanic said he thought I'd need special MB tools to get at the piston rings (like bolts w/ unique MB heads). Do you know if this is true? Or will conventional tools do the job?
I ask because everything MB makes is kinda pricey. Any insight will be greatly appreciated.
Thanks!

Answer
first off the 91 420SEL is a fabulous car, the last of the big W126's when MB had all the bugs worked out.  The biggest safest of all of the MB's of its time, and could hold its own today.  If the body and interior are in good shape  it may be worth fixing. A good set of metric tools shoudl be all you need to access the engine, there are a few part specific tools ( for the valves) but most can be worked around. The good thing about these old gals is that there are pleanty of parts around, lots used and in good order, how many miles on the engine, and what is the service history - both very important.
Good Luck