What are the many risks here, for a daily 80 mile round trip ? http://sanantonio.craigslist.org/cto/4302240084.html
I love Diesels. That said, the main risk is that if you do have problems they can be a bit more expensive to repair compared to the more common fare. Of the two I would be inclined to the Mercedes even though the VW would give better mileage and is newer. IIRC 1982 would still be in the era when Mercedes were well built and reliable if treated right. The VW is an electronically controlled Diesel which I don't much care for as you lose some of the simple reliability of the mechanical Diesel. Of course the VW is wrong wheel drive also. It also seems to me that Mercedes tends to stand behind their vehicles much better than VW. But there is a huge difference in age that one can't totally ignore. mike P.S. Given the age it would be wise to budget for a new turbocharger on the MERC.
I'd go with the VW. I know of one in the FL Panhandle that gets nearly 50 mpg (it's a '98 Jetta wagon). The guys that own them, love them to death! The gas cars, I wouldn't give a plug nickel for. The M-B is easy to convert to veggie diesel/biofuel, but they are as slow as a slug if they are not the turbocharged version...zero to sixty can be timed with a sundial!