Went to WEMA USA in Fort Lauderdale yesterday to pick up two of their excellent senders. (Don't forget to use code 551 when you checkout to get 30% off).
While I was there I had a chat with Alan the Operations Manager and the subject of Biodiesel came up. He pointed out that the only gasket material to deal with this was 'Viton". These gaskets cost $6 more that the standard cork/nitrile (Buna-N) gasket.
A quick internet search for "Viton" and gaskets pulled up "Quick Cut Gasket & Rubber Corporation, NY". After a conversation with Pete, a 12" x 12" sheet of 1/8" "Viton" is on its way to me.
BioDiesel info here
Another call to NMA provided a source of "Haysite" which is recommended as a support for the tanks (5200 onto the aluminum - read the David Pascoe article here). They can machine any shape you want. Contact Vick.
Sometime it almost looks like I know what I'm doing.