+1 for @stickfans. I made a purchase of a game board from him that the postal service damaged. Despite this misfortune, he was very nice to deal with and communication was excellent. Definitely a seller of good and honorable character.
What makes you think the entire body is just fiberglass? There is a 5 letter marking (PDCPD) on the inside of the cabinet just below the monitor service door.
Bondo isn't meant for structural repairs like this - it is just a body filler for smoothing out panels before paint and a somewhat shitty one at that.
I will be testing an MMA repair product on an Astro upper control panel housing that has split in the center. The big selling point of MMA...
European ebay sellers usually have them and are willing to sell on their own. I agree a clear one would be cool (I wa t blue), but if you are just after a clean one, that is your best bet. If you can't locate a seller, let me know.
What's wrong with your outside cover? Since there is no grain to the plastic, you could gently wet sand it with something like 2000 grit and then compound and it would probably look new.