Crosman 1077

I just received a Crosman 1077 from a friend, it was quite rusty so I sanded down the barrel and I sprayed the plastic stock with rubberized black spray paint. It doesn't work, when you put a co2 cartridge in it it all comes out right away. I took it apart and holy cow it's almost all plastic .Can I get this thing workin again or is it even worth it? And then I'd have to do something with the barrel too. Any thoughts?
 
Well I ordered some parts from Crosman ($11.76) and replaced the tube bushing, piercing pin, end seal and valve seal. The end seal does not look the same as the original, the original was flat on one side, this one is not. The parts list shows that the valve has a valve washer and valve "o" ring in there but my gun did not have those in it and when I tried to put them in I could barely screw the guide collar back on and the valve stem would not move, so I took them back out. The co2 still all leaks out rather quickly altho not as fast as before.I think I'm about to toss this sucker.