Thanks for all the responses. It is nice to know this is not a unique problem, and I guess I am lucky the driver's side seems to work better than the one on the passenger's side. I have priced out the seat belt units but I don't know if this is a DIY candidate. I would like to know a moderator's opinion or one from anyone who has done this before. Don't want to set off the cartridge device, etc.
Many old threads seem to agree with TobiasMB
but I have also seen many that really like these cars. I am one of those so far. Of all the MB I have owned this is the by far the best S Class, family sedan I have driven!
I managed to get a VMI from a local dealer, so I have much of the history of the car and many of the historical problems have occurred on this one. The only scary item is the EV does not seem to have been replaced, so I suspect I will have to go through that expense at some point. Wiring harness (engine), close-assist pump, power steering pump, push button control panel, rear window "lift motors,other" (three times), rear engine seal, distributor caps, etc. have all been replaced at one time or another. Harness was the latest at 96,000 miles. Other than seat belt problem, all else works, and car is very strong on the highway - LOTS of power.
One other tidbit, the Service Advisor at the dealer who sent me the VMI was told by MB USA regional rep he should NOT have given that to me. According to him, VMI's are Mercedes Benz property!!! Whatever happened to full discloser responsibilities? MB USA seems to be scared of litigation if this is truly their position on VMI's. Thought some of you might find that interesting.
Great site! Thanks again for the inputs.