aaron2874 ,
I just pulled my cap off my old fuel cell and looked at the RTV around the inside,the rtv looks unharmed by the fuel looks and feels the same as the portion outside the cap. I think it has more to do with the plastic,I noticed the clear plastic getting cloudy after about 2 weeks.I continued to use the cell for several months with no problems of course I was using about a gallon a week.
I did not fly for several weeks and had 1/2 gallon just sitting,BTW the fuel stayed clear but the plastic got worse not soft just real cloudy
when I used the fuel next flight both of my engines would not fire,I had a new gallon with me I pumped the old out new in and both fired just like normal. I am using 15%

Jimmbbo , get back and post in 2 weeks on the cell. Maybe it was the yellow milk cap ?dont seem to be soft or eaten