robthebox said:
Bob, you mentioned the thick yellow grease .... does it go runny when heated up?
I haven't tried heating the bits, but a bit of heat is a good idea if the unit is intact and all the wiring is OK.
This is the stuff I was referring to:
When you try to engage the difflock . . Can you hear the motor trying to turn the output gear and the rack ?? If you can I guess it could be made to work with some heat and maybe some oil injected through a very small hole as you suggest.
Something like the '3-in-1' spray would be my choice rather than 'WD40' that leaves a hard coating over the parts.
Where to drill the hole, though,

Probably onto the gearwheel, spring and output shaft, i.e. into the side near the axle-end. Then plug the hole with some silicone sealant.
Still best to remove the whole unit intact - if you have the patience
I still have the bits from 'Pentland Cruiser's' Actuator, I'll try heating the grease and see what happens.
I'll report back

.
Bob.