We have a 1990 OA model 440. Very pleased overall. Our boat had some cosmetic blisters when we bought it. I repaired them and epoxy barrier coated...nothing serious and they haven't reappeared. But you might look for that on a survey....and be aware that they will collapse and disappear within 30 minutes after haulout...so difficult to spot. Telltail on bigger bumps is cracked bottom paint. Zero issues with above water line hull. No window leaks.
I replaced the cutless bearings right after purchasing the boat...normal maintenance item. Had the Maxwell windlass rebuild by a gent in Seattle. Redid the black water plumbing to PVC and switched to fresh water flush....eliminated 99% of the old boat odor. Space heaters on our boat had a safety recall, but previous owner had installed reverse cycle AC unit, so heaters not required. Faucets were Taiwan units and difficult to source rebuild kits. Easier to replaced with big box store and RV (shower) items. Boat likely has Twin Disk transmissions which are virtually bullet proof. The Taiwan props on our boat ran a lot better after tuneup and rebalance.
Otherwise no issues. Monk designed some nice riding, dry and efficient hulls for OA, so you'll be pleased in that category. With exception of sink/showers, virtually all of the fittings and systems used high quality parts that are easily located. We looked at a couple 42 sedans before going for the sundeck...very attractive layout.
There are some part numbers listed in the OA section here on the forum. I'm trying to get OA to sponsor an owners forum on their web site. Haven't heard back from them. By the way, the Seattle dealer used to provide a list of every known boat and owner if you joined their owners club. Might be a place to find folks running the 42.