Has my air compressor died?

[Jonathan]

Is it still the same with all the air drained?
Have you tried checking/swapping the start capacitor?

Yes it's at atmospheric pressure and I doubt it's a problem with the start capacitor given what I've just found, but I will check that if it still doesn't work.

Also I forgot to mention that inside the cylinder there is some black dusty goop. Could that be the remains of an O-ring? There are 3 springy metal rings on the piston. I should find a manual...