The trim is just trim. The windsheild on all newer (W201-W124 and on) MBs is glued in. They are difficult to replace if using an OEM glass -- most shops will try to sell you an aftermarket because they are about 1/8" shorter and easier to get in. Stick with the OEM, they are thicker. The windsheild isn't self-aligning like the american ones, it has to be centered manually and marked with tape to get it in place correctly -- they may have had to put it in twice if it was crooked the first time, and the factory glue only has an open time of 15 min. At least they didn't charge you for it!
They may have had a problem with the trim if they used an aftermarket glass, as it is difficult to get the trim flush on the glass -- the trim snaps into the rubber "seal" -- really a trim retainer -- around the glass, and if the glass isn't factory thickness must be forced down to the very bottom of the slot to seat properly.
If it leaks, make them replace it again -- insist that they use the factory glue and clean the body flange properly.
The older benzes had a "lace-in" seal, which is very easy to replace -- they may have been thinking of that job, takes only about 15 min if you know what you are doing, rather than the couple hours maybe for the newer ones.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!