Folk, I am trying to determine which oil weight and how much to add to my Cat D4D with a manual transmission. I see posted online SAE 30 oil weight along with 85W oil. The SAE 30 seems to thin for a manual trans (seems appropriate to a hydrostatic trans). The SAE 85 seems incorrect as I would expect a multiweight like 85-140 or something of the like.

Additionally, dumb question but is fill on the side of the transmission or top next to the dipstick and shiftlever with a round plug having a hex-female cutout? Trying to prepare myself for how long I might be living under the tractor to change the trans oil since it was white when I checked it yesterday after running the tractor briefly.

Thanks for the help.