In the US find a rust free 250D merc, I'm sure they do still exist somewhere. They run veggie with no changes and run forever. When I say 'run', I of course mean 'amble along'.
You can run the younger TDIs on veggie, TDIClub.com has a few doing that.
Not sure about the PDs although I'm sure someone will have tried.
My dad has experimented with veggie in his 2011 1.6 CR TDI too
