I will add this... If it is adding points while holding the ball on the flipper I think you can narrow it down to the hoop (most likely) or the ramps (least likely) as there are only a few ways to score points in that game.

There is an opto across the hoop (you can see them near the bottom of the clear hoop plastic, they attach to the metal base plate) that if it is misaligned could be just off enough to give you the apparent break to score points. With the glass off, go into the switch test and look for the hoop opto switch. I would then see if a small nudge of the ramp is enough to trigger the switch. If that triggers the switch in the test, align the optos and repeat trying to trigger it with the ramp movement. Once they stop triggering the switch with ramp movements I would see if your problem has cleared up.

That foil or tape around the basket could easily block the opto, making the game think a ball is always going through the basket. That is also manifested with the knocks down the freethrow call-out when passing by that gate (picture two). That gate is hooked up to a coil to act as a diverter when you have in the paint lit. When in the paint is lit the coil turns on and keeps the gate from opening making the ball bounce into the pass holes rather than continuing around and up the ramp leading to the right flipper. The switch error you are getting, I think, is from the right inlane roll over switch. That will cause other issues on your game, but not anything you have described. It is normally a sticky switch, I have fixed them in the past by cleaning them, but is a temporary fix and normally is replaced soon after. Check to make sure that you don't see any broken wires coming from that switch. Do you know how to get into the switch test menu?