These types problems are related to processing the WVO, not the common rail. I have a friend who did probably 200,000 miles on WVO sprinter that had a common rail, but he always carefully processed his WVO. I'm not claiming the 2.0 TDI likes WVO or anything of the sort, just sounds like a bunch of WVO haters in here haha.Get a little super heated water coming out of the direct injection and watch how long things last. The indirect injection of old doesnt have that issue.
It was pretty easy around here till the filta type companies started popping up, and recycling companies started to pay for fry oil. Kinda changed the landscape over night.Just sourcing the WVO seems like a lot of work. Let alone operation issues. I bought an IDI Volvo years ago with the intention of doing a greasecar conversion, but collecting enough oil was too much of a pita.