As mentioned, removing the rear side windows is not that difficult. I have a thread on my own experience doing so with pics as well as the rust repair. If you can do the work, it's not too bad.

Same with the AC, thought it was the evaporator, turned out to be the compressor seals instead. Barrier hoses if original are also culprits, o-rings etc. New compressor, hoses, condenser and drier and the system has been running perfectly since with no leaks and the original evaporator. If it's a keeper, do it, these are such wonderful cars, it's hard to give up on them.
Good luck

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)