Flipper buttons unscrew from the inside of the cabinet. There's nothing to do with the plastic.

The u6 error could be the rom or could be something else. Start by replacing the rom since its so cheap then see. Johnwartjr on pinside sells them.

It's not only two years old. Those chips are not made anymore nor have they been for years. The roms are cheap to exchange so start there and see. If that doesn't solve it you may have a rom socket problem or other board issue.

The nut can be tight but turning it is the only way. I've never damaged a flipper button removing that nut.

There is a special plastic tool to take the buttons off but a large enough socket will work. Honestly, they're tight but not tight enough so I use needle nose pliers to remove the nut on the button. It's very easy and you can usually clean the up enough to not needing to replace unless they're damaged.

On a side note, almost every new button I get nowadays needs some filing to the inside as they all have some sort of hang up. Anyone else notice this?

I use a pair of needle nosed pliers to turn the nuts that hold the flipper buttons in. This works pretty well.

Just grab in a corner, and twist carefully.

I can program a ROM for you if needed.