Rear Window Seal on '54 Flying Cloud

[55AS]

Rear window has leaked in the past (judging from water damage inside). May still leak - not yet tested. I know the gasket is marginal and it appears the P.O. tried to apply some sort of sealant in the past. I have read that the proper fix is to remove the entire window frame from the trailer in order to replace the gasket. I also read that many of these frames are held in with screws. Unfortunately mine are riveted (with LOTS of rivets).
Questions:
1. Can I apply sealant as a temporary fix?
2. Assuming I need to remove the entire window frame, how hard is it to drill out this type of rivet?
3. Assuming I get the window out, can I reintall it with screws instead of rivets?
Thanks!

[55AS]

On closer examination I believe the window frame may be attached to the heavy flange riveted to the shell with fasteners hidden behind the gasket. Only the rear window has this flange (see pic of front window attached here). Anyone know for sure? Once I remove the gasket I will be committed.
Thanks in advance...

[55AS]

Turns out the rear window is different from the rest due to its design as an escape hatch. The PO had caulked it shut but it was pretty simple to defeat this. VTS suggests using a foam gasket to seal the "outer" frame and a "backframe" gasket to seal the inner one. Parts ordered.