I'd agree with the poster who recommended changing the oil press sending unit, although you could have the oil press checked against the gage reading first if you like. I have a '91 300TE 4matic with 212k miles and I know how you feel. There is no safer feeling than knowing when the weather gets nasty my wife and kids are driving around in one of the best snow and slush cars ever built. They have their problems, though. I just spent 3 hours this weekend pulling the heater blower out to fix a loose plug connection. The good news is I didn't have to blow $300 for a new blower motor with fans.
BTW, I just remembered, I had to replace my oil press sending unit for the same problem! Scared the hell out of me until I replaced it, worrying the engine was going to lock up.