When you get done farting around after nothing has worked send the tank to Gas Tank RENU - USA nearest location. Unfortunately none in CO but check the dealer list for closest. They coat the tanks inside and out and they are guaranteed a LIFETIME.

The shops on that list are run by really superb, knowledgeable people. I have been going to the one in So. Cal. for decades. They work regularly on old cars too. I'm certain they could mod or repair as needed.

But the imploding IS a problem that needs to be dealt with. If no mod is made it will do it again so ask them to fix that. These guys know what to do without guessing.