SOunds like, if the velocity is extremely low, it might need a new main spring. A spyder spring will probably work, if not it could be clipped.
The paint is probably your problem, the porting system on barrels have very little to do with the flight of the ball. Run good paint in it and it will be fine.
The cup seal may blow on you, again thats a spyder part(if your a good machinist you cna probably get anything spyder to fit in that gun)
aS long as there aren't parts that can't be replaced(in your case MADE apparently

), the gun should still be fun to play with. Ypu might check the detent system btw, it may be dying.
Post a pic, I'lld like to see it.