This may not help much... but I had a TEAC T1 repaired (new laser) by the local factory service shop. The problem (wouldn't read discs, at first just a few, then most, then all) recurred after three or four months.
Had two other shops look at the unit. They tried some adjustments. Nothing really helped. Then I was given the name of a new technician a few hours away. He fixed that transport, boy. It worked like a charm off his bench, I used it, sold it, shipped it and AFAIK it's still working.
Conclusion: it really helps to have a technician who knows what he's doing, and he doesn't necessarily work in the factory service shop.
Had two other shops look at the unit. They tried some adjustments. Nothing really helped. Then I was given the name of a new technician a few hours away. He fixed that transport, boy. It worked like a charm off his bench, I used it, sold it, shipped it and AFAIK it's still working.
Conclusion: it really helps to have a technician who knows what he's doing, and he doesn't necessarily work in the factory service shop.