Just had another look at it, the diode has been removed anyway so it should perform the same as the original.
Do any other WH20 owners have this problem?
Before I rebuilt it, it must have been aimed slightly different, as the ball used to hit the top of the flipper then roll up the inlane and back down (good for spotting river letters)
Maybe I just need to adjust the aim of it, but it is still way over powered 

Maybe a 24-900 coil?