Break off a wooden matchstick to help fill the hole?

Hello Cherga. Curious, I have a Gottlieb/Premier Monte Carlo too.

This is the procedure I use for the top of the playfield - Add dowel pins for stripped playfield holes. Your posts will be rock solid if you use this method, but you do need to be careful!

"If just thinking about drilling into your beloved favorite pinball playfield gives you the heebie jeebies, or you don't feel comfortable doing this in situ surgery, use the toothpick method and skip this section.

Almost every pinball machine with lots of use will develop posts that won't stay in place. These are typically the posts that get the brunt of the pinball strikes from the pinballs hit with the flippers. This method works well if the bottom of the post is bigger that 1/4 inch - this is so the post will hide the obscene dentistry you will perform on the playfield. Here's how to do it:"

http://www.pecospinball.com/my_first_full_pinball_restore.shtml#The%20Seventh%20Battle

I have been using the toothpick method for under the playfield stripped holes. I don't want to drill a hole right through to the top of the playfield.

https://pinside.com/pinball/forum/topic/stripped-screw-hole-repair-one-way-to-do-it

Concerning the acorn nuts - make sure you use an ignition wrench to hold the quarter inch "nut" on the playfield post before taking the nut off. If you want to keep the machine "pure", as in how it came out of the factory, use the acorn nuts. If you're not concerned, then use the rubber.

Like Pecos said, loose posts are not unusual for machines with lots of plays.

If you are placing an order with PBR, they have sell wrenches for holding the post nut.