Yup, the seal itself is not perished - it's the adhesive that seems to be the issue. It's happened on the driver's side previously and I managed to stick it back on. The other E46 M3 I had suffered exactly the same issue.
It's one of those niggles that can totally ruin my enjoyment of the car. If I see the door seal is a tiny bit adrift in any place, I turn into Patrick Bateman.
