If the bore is good, it's worth fixing. I bought my phase 1 1377 and found the guy had really oiled it up so the seals would work, but in a day or so I'd shot out enough oil that the air would go right out the barrel as I pumped it. I just bought a whole new 1377 valve from Crosman. It was less than $10 at the time. Gun works fine now.
Yours looks a lot like my vintage 1377. The older Medalist was shorter with a different forearm and auto cocked when you pumped it, so no need for a cocking knob.
I plink, therefore I am.