[RSBob]

We have two different interpretations of your problem.
1. You cannot close and latch the window, or
2. You cannot get the seals to fit in the window frame.

When I backdated my 82 to opening rear windows I installed new seals and they were tough. I ended up using lots of dishwashing soap and bicycle tire levers to get the seals/gaskets to fit. Like the others said go slow and use patience. Also the Windows didn't want close, so I pushed slowly as my wife pulled the inside latches and finally got them closed. I too left them latched closed until they relaxed. With time they became much easier to close.