Rear window regulators absolutely can go out, I replaced one a few years back, think it was from rockauto or something, tho I suspect it may have worn out sooner than normal bc my dog sits in the back and learned to hit the button to roll down the window to stick his head out, but he didn't always let go of the button when it was down. On the driver's side, the track tape is broken but it still works as long as I stop when it's down, otherwise I have to thread it back in. (Yes, I will get a new one someday..)
Mine is an 89 New Yorker should be mostly the same car. Your ac system will be 38 ounces but that doesn't matter much since you will not be using r12. If you use r134 you may have to switch to Ester or PAG, but I'm using "Envirosafe r12 substitute". (Sshhhhh..!) And you only need 12 Oz or so just get it up to where it's running 45 psi or so on the low side. So you know, this compressor doesn't cycle, it stays on with the ac switch and the cooling fan cycles instead.