The odds are a few possible faults here but I am no expert, firstly check all the breather points on the back case, this would include checking the tubes are clear to both F/Drives, the oil transfer is often blamed on the top pinion seals but this I have found to be a lesser reason, the common problem is fine cracks in the main case after years of Scraper or Ripper work, the best thing to do if things are all running well, is to fit a new copper gasket to the fill plugs then tighten firm and forget about it, always stand off to 1 side when you check any D8 or D9 F/Drive fill/level plugs as there is a great chance of getting a soak, I have found the breather tubes to the drives to be cracked in the past also, if it's got to much oil in it's a lot better that no oil, don't make work for yourself until you have to pull things down. tctractors. p.s. I often do a simple test after rebuilding the back ends by hooking shop air into the F/Drive breather position at around 5 to 7 psi and check for leaks into the main case, they soon show up.