on my Tales from the Crypt, I found that you can loosen the whole assembly, and turn the scoop kicker slightly left or right and get away from the middle drains. If the coil and mechanism is weak, it could account for centre drains because the ball is only shooting out at say 70 percent, or it could just be a simple left or right adjustment if everything is still working to its correct strength.
Loosen the assembly off a little and turn the whole mech slightly left or right, then tighten. Sounds like a small rebuild is probably required. Sounds like its a bit weak if its inconsistant.
It should be very simple. I did the same when i added a cliffy to my Tales Crypt machine.