Like Forced stated Viton is a brand name of hose, which is made by Dupont.

www.GreaseWorks.org sells viton hose kits for all MB models. Unfortunately viton isn't cheap even if you buy it in bulk, so the kits are a little spendy. I've had one of their kits on my wagon for three years with no issues what so ever. I also have never had problems with the injector return lines leaking.

Changing hoses before running biodiesel isn't crucial. It will eventually eat through the rubber lines, but it won't happen immediately. It may take up to a year. But you will eventually need to change them.
The other thing you will want to have on hand are some extra fuel filters. Biodiesel is a good solvent, it will clean out your fuel system, which will clog your fuel filters. So be ready to change those out a few times after you start running biodiesel.

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