Different Tranny's, different oil
This is from the Yanmar Manual:Transmission Type 1GM10, 2GM20(F), 3GM30(F)KM2-C: SAE #10W-30, CC class .25 L KM3-A: SAE #10W-30, CC class .3 LTransmission Type 3GM35(F)KBW10E: Dexron-ATF .7 LTransmission Type 1GM10, 2GM20(F), 3GM30(F)KM2P: SAE #10W-30, CC class .3 L KM3P: SAE #10W-30, CC class .35 LTransmission Type 1GM10V, 2GM20(F)V, 3GM30(F)VKM3V: SAE #10W-30, CC class .8 LThese transmissions were changed in August '85based on your serial no. KM2P 1GM10 03413 and after Aug. 1985KM2P 2GM10(F) 03567 and after Aug. 1985KM3P 3GM30(F) 01888 and after Aug. 1985There is a chart in the manual that says to use the "Same lube oil as for crankcase"We have always used the same oil as in our engine. This originally was 30W and we have recently switched to multi-grade 15w-40.I would not suggest that anyone switch to a pure synthetic oil on an older engine. The oils quite often will cause an "OLDER" engine to weep. If you start out with these oils it tends not to be a problem. For some reason Yanmar has never recommended synthetic oil for these engines. That may have changed with the newer engines, but I would check first.