Make sure all stepper units operate correctly. they do seize up over time . Only use singer oil on the metal pivot points and operate them using the coil plungers, only use a drop and then wipe all the crud that will weep out.  They should be working freely, also these unit have brass contacts clean with 600 wet n dry clean up with alcohol and use the smallest amount of inox mx6 grease, jaycar carry this stuff . regarding the game over problem ,check ball count unit and /or player unit in backbox. and check the lock relay inside cabinet.  Not sure about the fuse blowing but check the playfield coils one may be seized check resistance anyhow anything less than 1ohm is RS and maybe a coil switch is set to close and locks the coil on ...And good luck most EM problems can be seen by eye so take your time and work thru it