Bu**s**t. It does too eat rubber. No if ands or buts. don't take my word on it:

http://216.239.41.104/search?q=cache:1x9Q-cfKjSEJ:www.biodiesel.org/resources/reportsdatabase/reports/tra/19950101_tra-051.pdf+rubber&hl=en

http://www.biodiesel.org/markets/gen/default.asp

http://216.239.41.104/search?q=cache:8Fjnauf5USgJ:www.biodiesel.org/resources/reportsdatabase/reports/fle/19981001_fle-015.pdf+rubber&hl=en

Hardly inconclusive. If you are using a 20% mixture you are fairly safe. As you approach 100% forget it with most "rubber" - you should at least consider replacing those lines with the likes of viton.