As with any old computer, I wouldn't expect to get any help from Apple in the way of parts. Any parts you are able to come across will be new-old-stock, used parts or parts pulled from other machines yourself. Being technically inclined or knowing someone who is will be a big help if something you can't live with needs to be repaired. That's part of the reason why so many of us have such huge collections. It's to keep us in parts when things start breaking down.

As to the hinge, it depends on the hinge. If it is held together with screws, they sometimes loosen with use and need tightening. If there is pin holding it together like a door hinge, the pin may be slightly bent from abuse. I don't know exactly what type of hinge holds the Wallstreet together so I really can't say precisely what the problem might be, just give examples of the two hinge types I know of from other brands of laptops. The laptop I am using now has hinges held together with screws and both of them actually loosened up and fell apart while the machine was still under warranty. The biggest problem, I think, is going to be finding disassembly instructions because laptop makers can be diabolical in placing screws and fasteners and the order they have to be loosened to get the case open sometimes. The clamshell iBooks are particularly infamous for being hard to open.