The Gulfstream is a great boat, but of course you’ve got to do your homework on a decision like this. Think hull first, engine & steering second… after that electric (wiring) and electronics then plumbing (hoses) cushiness & eisenglass and miscellaneous items. I think that is about the hierarchy of expense if something is broken or needs repair.
Definitely check out those angled cabin windows. I’m betting one or both have a leak, if they haven’t been fixed previously. Also the through hull fittings on the ’96 were plastic originally. If they’re cracked they must be fixed. A real PITA job, but still not a deal breaker. I think with any used purchase it’s not what you know, because you can manage to it. It’s what you don’t know and find out afterward that is the real trouble.
Also figure out if a 250 is enough HP for you. Search the site for discussion of this topic. There are equally good points to both sides of the discussion, but only you can decide for yourself is 250 is enough. Good luck.