FWIW - My 99 gets ~10% less fuel economy burning B99 vs D2.

The only issue you should have is gelling. If an oring does fail, it was already deterioated and would have eventually failed burning D2 as well. Bio can hasten the process. I doubt 2.5 tankfuls would cause much of a problem.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)