You just need the right screwdrivers.

Always use a quality parallel bladed screwdriver for removing slotted screws, never anything with even the slightest taper to it.

For my Gottlieb EM games I religiously use the two following screwdrivers and have a few spares of each.

This one has the 1/4" wide tip:
http://www.amazon.com/Gardner-Bender-SCE-257-Electricians-Screwdriver/dp/B000MR404S/ref=sr_1_fkmr0_2

This one has the 3/16" wide tip and comes with a quality #2 phillips head as well. I can get these off the shelf at my local True Value Nutz & Boltz hardware store for about $13.
http://www.rakuten.com/prod/gardner-bender-insulated-screwdriver-set-2-pc/222806596.html?listingId=147093369&scid=pla_google_HomeandOutdoor&adid=29963&gclid=CP6I9fbmnL8CFa9r7AodPSoA-Q

I use the 1/4" tip on most of the screws on a Gottlieb EM game except that I find the 3/16" tip works best on the smaller screws holding the flipper coil brackets and the pop bumper coil brackets.

I rarely strip any screw with these quality tools. In time they may wear out depending on how much use you give them. They are also magnetic tipped which is a huge plus.

Mike O.