I had removed the frame, cleaned off all the old silicone seal, and scuffed up the acrylic gel coat at the seal contact point with sandpaper in the hopes that it would give the silicone seal something to bite into. Unfortunately it did not work and it is once again leaking. I will have to remove the frame once again and next time grind through the gel coat for a much rougher contact surface. I am considering applying a bead of epoxy to bond and seal the metal to the acrylic base and then caulking over the epoxy with silicone seal. I might also drill four holes through the metal track (where the door rollers don't travel) into the acrylic base and drive self-tapping SS screws.
Previous to my current shower, I had another (economy model) MAXX shower with acrylic walls. I had to dismantle it and redo the seal on it. In that case I added large fender washers to the existing screws that held the sections together and applied another bead of silicone further back in the joint. After the unit was back in place, I applied a final bead that was just cosmetic.
I would be interested to know what you may find and what MAXX may have to say on the matter. I wrote to MAXX and they did not even bother to reply.
As for your question WRT removing the old silicone from the gel coat, I don't think you should have any problem since it doesn't really stick. There are cleaners made specifically for silicone seal if per chance there is some residue.