Dave -

I think I can actually answer your question

I have done the exact same thing in my '87 300TD. Following a compressor seize-up 2+ years ago, I flushed the entire system and replaced the compressor with a junkyard unit. For lubrication I used Polyalpha, an oil being sold by acsource.com at the time. It's a POA, or PAO - a synthetic refrigerant oil which works for both R12 and R134a. I initially ran the system with R134a for a few months because I was nervous about leaks. Once I had things under control, I evacuated the HFC and replaced with R406a - an R12 substitute. No change in the oil required. Everything has been copacetic, system works great (except for the evaporator leak - I'm planning to replace during my holiday break later this year).

So what you're proposing is quite possible, given the right oil. I think BVA is very similar to the oil I'm using, though the viscosity is different. I'm considering using it when I fix (for good) the system in my 300TD.

- JimY