I only have experience with Viton in the fuel return lines, what 3 mm?
Viton seems like a softer rubber and is not made in layered hose, that is with a nylon reinforcing web inside like other hoses.
If they made Viton inner hose with a nylon innner reinforcing layer and Buna outer rubber that would be the best of both worlds. Maybe someone should invent a new hose?
I did a search and found this info re: Viton hose sizes (and lengths?)
Length/sizes of rubber->viton fuel hoses?