Job #1 = open the backbox, and cut the battery off of the MPU !!!!
This is super important, as once you warm up the game again, it will cause that old battery to leak it's alkali all over the MPU, killing it. Remove it today.
Job #2 = New Ball
Don't roll that old ball around the playfield another minute. Old balls have corrosion that acts like sandpaper.
New "super shiny" balls are $1.50, buy a few spares, they get nicked up fast - and nicked balls wear down your playfield.
http://www.pinballlife.com/index.php?p=product&id=1325
Job #3 = Wax
Wax that game with a good, non-silicone, non-liquid, paste wax.
Wax the playfield, the ball guides, everything.
If you don't wax the game regularly, the ball will be riding on the paint - wearing it off.
Blitz is probably the best wax, it's always behind the counter at the auto parts store so clods don't steal it.
http://www.pinballlife.com/index.php?p=product&id=2589
Job #4 = New Bulbs
You probably have a bunch of bulbs burned out, and a bunch more that look shiny black.
Replace ALL the old #44 bulbs with new #47 bulbs. The #47 use 40% less electricity, so they will help out that old overtaxed powersupply.
A box of 100 bulbs is like $7, money well spent to protect your game.
http://www.pinballlife.com/index.php?p=product&id=2523
Job #5 - New Rubbers
Nothing makes a game play great like new rubber.
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Manual:
http://mirror2.ipdb.org/files/1823/Bally_1978_Playboy_Manual.pdf
You won't need this yet, but in the future:
https://pinside.com/pinball/forum/topic/vids-guide-quick-bally-driver-board-repair-bulletproofing