hmmm, something sounds familiar. just recently I replaced both front struts in my 190 d. my sister's boyfriend helped me, and because he never drove a MB, I let him take it for a spin. When he came back, he asked if the car always takes so much effort to keep in straight line. After driving it myself, I could not believe how much out of alignment it got. The car was trying to go left and right all over the road. So I went to the alignment specialist. Guess what? alignment was fine. So the next thing was to get two new tires (yes, from tire rack). Because after driving for 20 years I firmly believe that Michelins are the most overrated and overpriced tires ever offered for sale in the USofA, I bought a pair of Yokohamas (same performance as compatible Michelins at 1/2 price). Problem solved !!!! car drove like a charm. For a month. And then the old problem returned. Front end just felt loose. Two separate mechs went over the car and said that front/rear suspension was just fine. Now, two month later, its still a little loose, but driveable.
As for your problem, I vote for the intermittent caliper problem-sticking but only occasionally and after your break fluid gets hot.
By the way, don't get sucked into the "more expensive is better" trap. essentially, all major brands in the "all season, high performance, and touring" categories deliver the same performance. the differences are so small, that have to be measured with a stopwatch on the track under controlled conditions. I guarantee, that when driving the same car, nobody of the above could distinguish between Michelins, Dunlops, Yokohama mamas, or Bridgestones (I agree that Firestone is BAD).
Ok, now come and tell me how I'm wrong and that You definitely CAn tell the diff. Right!
1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"