I'm getting 5.12V at TP1 on the solenoid driver board.
Maybe I should check the MPU board itself.

Yep! a LOT can happen to the voltages in between boards, loose connectors, poorly crimped pins, corrosion and burn out etc....
While the Power supply might have 5v-12v leaving it, it doesn't mean the mpu (& other) boards are receiving 5v-12v  ;-)
It's always best to measure on each of the boards, as most boards have their own voltage regulators and associated components which can fail....

The flippers themselves haven't ever been weak (I don't think).  They still kick just as hard as ever. It is other solenoids that have the problem - i.e. anything that is "driven" by the boards.

Flippers are typically on a different voltage supply to the playfild solenoids, and flippers are not (never?) controlled by the driver board, so that would highlight the different 'kick' they have....

anyway, good luck with the new board, at least it will definately prove your old mpu (or not).

MM.