Just came across this the other day at a tractor shop. Supposed to be very good, but then a salesman will tell you anything. It's called CA-40 fuel additive, the price is high, Farm Pro $39.00, on-line $35.00 but it treats 480-640 gallons.
If any one has used it can you tell us how you like it?
Here is a link
http://www.ca40g.com/home.php
Thanks
BG