[m22mike]

First off take a Ohm meter set at R1 and see if the coil still has a continuity. Terminal blade to case. If it is open, quit trying.
I have had very limited luck with the WD 40 thing, even the ones that started working sounded like crap, and the adjuster screw has very limited affect.
I have taken some appart and installed new diaphrames, however if the contacts are junk it still may not work well. Also rust can cause the plunger on the diaphram to get stuck.
From what you have done so far it sounds like it is Horn Works time, he does a great job too.

Mike