My conclusion is that the offending material was probably mold release that was not fully flushed out when the tanks where made and the whole affair is not related to Mo-Gas.
Dorsal. I'm not buying your conclusion and don't think you should proceed as if you've solved anything. Yet.

I developed no problems with any contamination during Phase 1 (40 plus hours of 100 LL use).
First fill of auto gas I used up in the same day. Next topping off with alcohol auto fuel sat in the tanks for 3-4 days. That's when damage was done. It turned the resign , not release agent, soft inside my tanks. After restoring both carbs , rinsing and going back to AV-gas I've had no recurrence and the tank resigns seemed to revert after rinsing and drying back to the correct state. I checked carefully and frequently. No leaks from the incident either. Luckily. Could your situation be different than mine. Maybe. But what if they are related? You may get airborne before it stops your engine this time.

I guess the only way to know is to repeat the process. Just be mentally prepared if the problem appears again. Keep Andrew close by. He knows the procedure now so no training required.
Proceed with caution. I know you will.


P.S. Something else to think about during first flights.
I did find glass fibers in my fuel filters for about 15- 20 hours into the test flight phase. I watched this carefully as others advised me this could occur. I changed filters twice during my 2- 3 hours of ground runs(finding the most fibers during this period) and immediately prior to first flight. Then every 4-5 hours until fibers stopped showing up in the filter elements. Glass fibers are invisible when wetted with fuel so don't look at your see through filters and think you are safe because you don't visually see anything. Change your filters and inspect for glass fibers. After 700 plus hours I still remove, dry completely and then inspect my filter elements for glass fibers. Haven't found any since early into the test phase but can't help still looking.