Repair fork or get new one?
If your time isn't worth much and you like to tinker (like me), at least take your current fork apart and see if there's anything you could do to improve it's situation.

That said, based on your description of it's problems, I think you should buy a new one. And I actually mean new, in this case. Normally it's better to buy a used bike than a new one, but with something that's as age-sensitive as a suspension fork, I'd buy a new one (and take care of it, maybe get a stanchion boot).

As to what fork you should get... take note of the specs of your current fork (brake options, wheel size, stanchion size, travel) and get something similar. $150 will get you something decent.

If you decide to get something new, Amazon, Ebay, and your LBS are good places to look.