Also check the switches at the flipper buttons, they may need adjusting. Same with the EOS switches if the machine has them.
+1, My Tommy occasionally has the upper left flipper a bit slower than the lower left - sometimes it even fails to fire. I've found that the switches at the flipper button need a little clean, and a little adjusting so they both fire at the same time.
Well after claiming I'd sorted things out the gremlins returned again.
I've got to adjust the switches too - I'll probably replace them as they're pretty trashed.
