I did this as my was leaking - ended up taking the whole thing out on a nice sunny day, using mastic to bed the glass. The black internal trim is the hard bit which I think is what you are referring to. I cleaned mine then ran a small amount of washing up liquid around the part of the seal that goes in the aluminium v. Worked ok but hard working above ones head. I found it impossible to refit the small screws so used self tappers - initially just to hold it in place but the looked good so I left them. I put these through from the outside if that makes sense
