Quoted from Garrett:

It's great that game is trying to play, means things are in fairly decent shape.
I do recommend getting the schematic, Steve is an incredibly knowledgeable Gottlieb guy. I think he only takes checks or cash though, old school. It's really very difficult to work on these without a schematic.
http://www.pbresource.com/
Again, with the fact that the pin is an EM and has been idle, take your time and go through every contact. Look for coils where the paper has burned off and replace them such as the Game Over coil, it will also reduce the 60Hz hum that can be loud with old burnt coils.
The player unit in the back of the head should be gone through, the fingers and contacts on the disc and verify proper position.
Check the coil sleeves for cracking and cleanliness. And so on and so on....
For me, one of the most rewarding parts of getting an old EM is getting it running again. If you take the time now and go through everything and get it set up properly, it should run for years problem free.