John, thanks for bringing this back on topic. I will have to check the plate on the trans, just for S&Gs.
Let me add a few clarifying points for the group.
1. I do have and have read both the Yanmar owner's manual and service manuals for my 2GM20F / KM2P combo. Engine and manuals are circa 1988. Each specifies SAE 30 or similar multigrade motor oil to be used in both engine and the gear.
2. I do believe that there is a real difference between SAE 30 motor oil and ATF.
3. I would have used motor oil in the trans if in fact I had done the replacement myself. ATF wasn't even on the radar
4. I clearly specified on my haulout order the brand / weights of lube to be used in the engine and gear - in fact, I even provided the oil and filter. However, the yard disregarded my instructions and justified by stating they called Yanmar on my specific situation and YANMAR specified ATF. My guess is they didn't correctly identify the gear model if/when they called Yanmar last week.
Now...we all know that the probability of a Yard Error is pretty high. Bottom line....I think the yard owes me a drain + flush + refill of the tranny.
That said, I was curious if it is possible that Yanmar has revised their specs to allow ATF in the KM2P gear?