Prime Mover Model 15B

Been gone for a while. Working on a concrete buggy , prime mover Model 15B. Picked up off craigs list. Got it running. Needed to do a little machining for the clutch lever but I got that fixed ok. My problem is I dont know what oil goes in the tranny. It has two clutch's ,forward and reverse. Everything seems to work but I am reluctant to use it till I get the correct oil. I have looked on every site I can think of but no maintenance manual for this model. I located manuals for model 15 & 15A but almost nothing on model 15B.The transmissions are quite different. Anyone out they know anything about this let me know. Looking for plans for a Radius cutter for my Sheldon lathe, Seen how some are made on google so I would like to get the drawings and make one. All help is appreciated, thank you W.R.T.

Use a medium hydraulic oil....R&O 68 will do......if it has wet clutches be very careful of motor oils ....they may have friction modifiers .