I thought I would mention this because it comes up from time to time, where to get things like this. I have used the o-ring kits from Harbor Freight which are around $10 for a box of assorted o-rings. A whole box for what could amount to the price for one o-ring from a genuine Bosch distributor. I have used them on injection pumps and other misc. engine parts on VW, Cummins, etc. for years and have had no problems, which leads me to believe that they are good quality.
Make sure to at least get the HNBR o-rings for resistance to fuels and automotive chemicals, and possibly the Viton ones (which are a few dollars more) if you are going to be using biodiesel.
Also, while you're there pick up a box of copper washers for the same price and a box of chemical resistant gloves.