I don't have a model M but I have a model 40 which I think is the model just after the M and shares the same engine, etc. I haven't used it much in the past few years because I mostly use my Kioti NX4510 now. However, if I check the oil after it has been sitting, the oil level is always very high. But if I remember correctly, if you check the level right after it has been run, it will read normal level. I always figured it was because the oil in the inverted oil filter bell housing slowly drains back into the sump. That filter probably holds close to a quart of oil. So, when I do changes, I just fill with the spec for the engine (5 Qts) and it doesn't ever seem to change on the stick. I do lose hydraulic oil through the rockshaft seals but I don't think it is getting into the engine oil or the level would go up over time.
I just looked this up in the manual and here is what it says:
"The actual crankcase capacity of your Model "40" tractor is 4 quarts. However, as it will be necessary to replace filter element with each oil change, an additional quart of specified oil should be added to bring oil to operating level in crankcase at all times. Approximately one quart of oil will be contained in oil filter and oil passages while engine is operating."
I also found a paragraph relating to the All-Fuel version, but I think the point made about checking the oil level is the same.
"Do not check after tractor has been stopped for several hours, as the level will be higher than immediately after stopping engine, due to oil draining back from filter."
