Re: Aging zippers
Those headliners kept me from buying an early 80s Islander (the aging Volvo also had something to do with it) because I couldn't inspect the bottom of the deck hardware. I feel your pain.
I've had stuck cushion zippers on my Pearson and found an online trick of soaking the zipper pull in vinegar (using saran wrap to keep it there), then using silicon spray lube. That worked well enough for me to free them up. I broke off the pull on one zipper, but was still able to push the head using pliers.
If you don't want to do a full headliner now you could pull down the headliner and paint the interior of the deck white (instead of the dark brown that it probably is). The fiberglass that I could see inside Islanders (behind the vinyl) was generally very smooth. You'd only have deck hardware showing through, which isn't that big of a deal. That is a part-day project instead of a multi-day one.
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior