I'm totally late to the party as I just found this thread. I've now owned my TMNT Pro for 2 months and I love it. Especially Co-op mode with my 14 year old. I get that it's a bit on the tougher side, but I love the challenge and the theme is amazing for a 41 year old like me who grew up watching Turtles and collecting all the toys. I personally haven't seen any of these balls getting stuck issues on latest code 1.51, so I guess I can consider myself lucky. I got at least 900 overall plays too.
I will say when I first got the pin NIB, I did notice my first play through that the ball would get wedged in the lair pretty good and it wasn't the stopper preventing it, I just noticed that the lane itself was not wide enough by like a fraction to allow the ball to flow down to the left flipper lane. I don't know if anyone else has experienced that. I just opened up the playfield and loosen the screw from the bottom while pulling the lane and retightening. This did the trick.