That looks like much more work than on the 123 and 126 cars, but perhaps it's because there is no side felt? If t appears that the front seal wraps around the side on the 124 cars. Sorry to mislead you in my assumption they were similar.

Looking at the instructions and drawing, I'd sure as hell try to avoid having to drop the pan and drill out the rivets. Removing everything else appears pretty straightforward and may provide you with the room to work without pulling that rear piece.

As for rust, yes, I had some. The seals were completely dried out when I got the car so there was some serious leakage. There didn't appear to be much in the sunroof seal channel, though. I touched up with POR-15 as best I could without dropping the sunroof pan assembly.

__________________
Joel
1985 300td (sold)
1981 280SEL (4-speed)