Probably best to take it to a shop where they have experience working on older turntables. They might have rusted in there and can be loosened enough to get them out but then they're going to need to replace them. And who knows what else might need to be fixed once everything has been freed up.
That being said, it's a good, old classic turntable, and if you've got a bunch of records sitting around they'll probably sound okay. The shop can also give you an idea as to how the cartridge still performs. It might be just fine, but you might also need to buy a new stylus for it. The Mark IV cartridge is worth keeping though.
-Eden (I've navigated this slippery slope many times before)