Just drill out the lock and put in a new one. Many of the various locks can be found at Marco Specialties and other places. Some you can get keyed alike, or even a keyless style. A lot of people just try to get them playable, so don't worry - only a subset of the pinball hobbyists can take on full restorations.

Here is a good primer on the world of electromechanical pinball repair:
http://www.pinrepair.com/em/

The good news, is likely its just dirty switches. Old EM games that aren't played often, tend to get corrosion/dirt on the leaf switch blades. Playing a game, those are designed to rub against each side a bit to keep the contacts clean. Sitting for years, the contact between the blades is poor, many things can go away from just cleaning and adjusting switches, ball count is goofy, won't reset, score reels not resetting or struggle counting to the next digit, or game over / early switch close. A working game that sits and then doesn't work - 99% of time its switch contact related.

The game over right after a switch hit is likely a dirty/poorly gapped switch at the game over relay (gap being the space between two "leafs" on a switch - either they are touching = no gap, or too far apart, wide gap, or so dirty they are gapped correctly but not making contact across the dirt/corrosion). can be one switch or a chain of switches in a combination of relays. If after reading the pinrepair.com/em link and you decide not to try yourself, then you should have a pin repair guy come out for ~$100 and go through and clean the contacts and adjust the gaps on all the switches, clean the playfield and replace burned out bulbs. You may need new rubber on the game as well, 30 years and rubber gets brittle and crumbles or will break soon.

So Labor $60-120/hour depending on your location.
Parts - likely guess $40: couple 10 bulbs per box of #44 bulbs ~ $2 a box, rubber rings and switch adjustment tools, switch contact cleaner file, a small bottle of novus 1 for cleaning plastics/Playfield, get your stuff at Pinball life, easy to order, likely all in stock, good prices and Terry is just an excellent guy.

A game tech knows those quick maintenance things and likely get you up and running in an hour or cleaning and adjusting.

I'd encourage you to follow the pinrepair.com/em steps, and come back here and post progress or "I'm stuck, now what". We all started there and its actually pretty quick to learn the basics under the hood. EM's are simple on/off switches, and learning the path of on/off logic throughout the circuit of the path of switches.

General rule - don't lubricate anything. Attract dust, and mixes into binding material v. lubricant. You end up with gummed up plungers, pivot points, etc.

ipdb.org is a great place to start getting info on a game...
Rubber ring chart: http://www.ipdb.org/showpic.pl?id=601&picno=15981

Light bulb locations are not documented, buy #44 or #47 from pinballlife (a modern version of the #44 design; less power and less heat)

Shopping for specific Gottlieb parts should begin with Steve Young @ Pinball Resource. http://pbresource.com/
Steve's been around for decades, and is old-school paperwork guy, read his site instructions on ordering, you need the all-important customer # established by buying a small amount of stuff, paying the invoice sent to on paper in the box with a check only (no credit cards with Steve). Tell him you are a newbie, and be patient, Steve is a just-the-facts kind of guy, but the most know how on Gottlieb EM parts you will ever run across.