Probably. As I said, a tiny leak can let in a lot of air. As for replacing the pump, after 14 years it owes you nothing. I'd say you got your moneys worth. However if it's in good shape, no rust and will come apart easily without snapping bolts, and you can get parts, you may try a repair. But, although motor basics haven't changed, motors can be built to run at higher efficiencies today compared to 14 years ago. I think I would tend to go for a replacement and maybe even consider a two speed.
Al