check the rear of the solenoid driver board where the relay is soldered in for any dry joins, cracks in the solder around the pins.
check the left hand cabinet flipper leaf switch contacts, need to have tungsten tipped contacts that are making well, they may be worn?
can you post a picture of the flipper assembly, ideally the solder tabs on the flipper coil.
does the flipper move up and down freely by using your hand, both ways, like up and down on the playfield and up and down in the flipper bushing?
