I have the same issue. Those older socket head bolts are pretty soft and round off easily. The newer square drive bolts seem to be a much harder material, and Robertson drive bolts won’t strip as easily as Allen head. I’ve tried soaking, easy-outs, heat etc. with little luck. It’s not a bad idea to replace all of the old bolts with new, even if they seem fine now.
The plan is to cut the bolts through the slot in the collar, then pry open the collar slightly, enough to get it loose and off, then replace with a new collar. This worked in the past, but now I have a few more to replace. Your last resort might be to just cut the collars off and replace with new.
Good luck!

It lays flat. It is essentially a gasket between the metal body and the dome. It sticks to the perimeter and covers the bolt holes, so you will need to cut out the holes if you’re putting the bolts back in. Cut a V-notch for the corners with the rounded ‘lip’ toward the outside. Hope that makes sense.

I think mine had adhesive attached but double sided tape works as well. Use the bubble as a guide- the rounded lip should be just slightly larger than the dome edges (1/16” or so?) so that the dome lays on the flat part of the gasket. The ice just lays on top, sandwiched between the gasket and the dome. Of course all of this is entirely from memory, so I’ll have to double check tomorrow. Let me know if u need a few pics while I’m at it.

Sorry for the delay- have a few pics of the rubber seal finally.

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Thanks! I stripped and repainted it black, just to be different and to play off of the Team Canada colours. I used a polishing kit on the paint up to 12000 (yes 12 thousand) grit and I’ll be using that on the dome next. It’s a lot of work but definitely worth it. Dome isn’t really that bad but I made an led light to replace the fluorescent for the scoreboard and it seems to reflect the imperfections much more. Added the famous 3D printed nets, custom painted 3D printed cupholders and player names/numbers, custom Canada and USA boo/eject buttons, covered the dome flanges and bolt holes and made custom rivets to hold it all together. I need to redo the USA team though, so no decals on them yet. My favourite mod though is the lighted riser, it really saves your back having it raised up a few inches.
A few pics as requested:

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Stephane Lavoie did mine- awesome work. He’s not on Pinside but can be found on Facebook or via fb messenger.

Appreciate the compliments! It was/is a fun project, and I have a few more ideas and plans as well.
The cupholders were printed by the same guy that did my player numbers (see my other post above) but he isn’t doing any more for the time being. I believe the files are relatively easy to find if you want to print them yourself, otherwise there are a number of people who are printing and selling these. Airbrush paint wouldn’t stick so I just used Testors model paint on the raised areas.
If you aren’t satisfied with the decal removal on your dome you can always just cover the damage with ‘boards’ decals. I ran a strip of white vinyl on the flat part of the dome and it does a good job of covering that part up. There are sellers that make custom boards decals as well (with logos and advertising etc.) that would cover any residue left over.

If you’re not absolutely set on powdercoat, I actually painted and polished mine and it has help up fine for years. I used the ‘industrial’ version of Tremclad (black though) called Rustoleum in the US I believe, which is available in many colours and shades.