There's almost CERTAINLY 10 point switches on this game - probably rubber switches. Literally every EM game has them (or 1 point switches on a 4 digit game) I would suspect the fresh rubber is closing one of those switches. Find that issue and fix it and it will probably fix the 50 point issue as well.

Double bonus - like you don't have one of these games in front of me right now but go through everything that is supposed to activate the double bonus relay. Probably the BIG or BEN targets. Each one of those letters (switches) will activate a relay - go through all the switches in each of those relay banks and make sure they are cleaned and adjusted properly.