If you can find one I would buy it. I have a 1993 140 600 sedan that had a Western Diversified warranty that was really helpful.
I bought this car about 2 years ago with 60000 miles on it. In the last year I had the ighnition switch replaced($500), the power steering /hydraulic pump replaced($2700) and the engine harness($2600). All covered with this warranty.
I plan to keep this car another year or two and recently purchased coverage from Warrantybynet.com at 87000 miles. Its good for 2 years and another 30000 miles. It cost about $2400.
I reviewed the service done on this car with the MB dealer before I bought it to be sure that it had been properly serviced. I found out the the trasmission had been rebuilt and the evaporator had been replaced.
These cars are expensive to maintain and I would highly recommend some kind of coverage.