First of all, my thanks to everyone for your responses. I actually had a chance to get over to look at the tractor late this afternoon. I did check the oil and it was not milky and did not smell burnt or anything. However, I also learned that the oil had been changed only 2 hours ago (according to the tachometer hour reading), so I assume that could hide some issues.
I never did get around to checking the antifreeze, as we got to talking at length about the sickle bar mower (an MF 135 model number). It runs off the PTO, of course, but there was some question about my being able to use something else -- my main interest is my KK II rototiller -- with the sickle bar mower still attached. If I understood what I was told correctly, because of the setup, I must lock the mower's lift lever into the "maximum up" position (and there is a slot for locking it into that position) in order to be able to use the 3-pt controls with the lift arms. That would be fine. I just do not want to have to remove the mower every time I want to use the tractor for something else. (My plan is to use the mower to clip the pastures as I rotate the cows from paddock to paddock, so I want it to remain attached as much as possible. At the same time, I want to make use of the tractor for other things without a whole lot of on-off playing with the mower.)
Anyway, as for the rest of the tests, I did follow your advice, Ken, and it passed those tests. The only drips I could find did not come from the rear main. There was a bit of oil coming from the hydraulic control, which the dealer told me was most likely the O-rings at the one end, which made sense to me. Best of all, he offered to repair that unit as part of the purchase, if I go through with it. The other drip was from the right side of the steering box. It almost appeared as if the previous owner had put hydraulic oil in the steering box, as that is what it appeared to be. I double-checked and it really looks like the drip is from the box and not somewhere else. I can't believe that the steering box was supposed to have hydraulic oil in it, as I understand that there is no pressure in the box, itself, although the tractor does have "power assisted" steering. It is not a bad drip and I wonder if replacing whatever it is with the proper oil (which has to be thicker than what was coming out) might not stop the leak or at least slow it way down.
Larry, I did what you suggested and it performed well, although not perfectly: clutch did not seem to slip; gears seemed to be smooth-shifting; motor has lots of power on tap; did not find any signs of blow-by. (My Ford 660 has blow-by, but it does not show up under simple driving. I could drive around for hours and never have it appear, but if I run a plow with it, then the motor is covered enough to drip when I put it away. So, my driving the MF 65 around might not have proven much in the blow-by department.)
The only smoke I saw, of any color, was some black when I was testing to see if I could get it to pop out of gear. Put it into gear near idle; let out the clutch; suddenly throw the throttle wide open. No gears complained, but, just for an instant, I would see a puff of black smoke, when I first pulled on the throttle. I assume that I was just overloading the carb with fuel and it could not burn it all up right away, but would catch-up as the rpms climbed -- sort of like a diesel will do. Any thought that I am wrong about this thinking?
It did fight me a bit when I would engage the PTO. Not much, no real grinding, and if I took it slow, the PTO would engage without complaint. I was told that this is common on these old Masseys and does not indicate a problem. Also, the 3-pt lift arms had an ever-so-slight stutter as they raised, which I wondered about, but I was told that the Masseys used a piston pump for the 3-pt hydraulics, and that was the cause of the stutter. I could believe that as the stutter I saw was so slight that if I had not been watching very closely, I never would have seen it. But, any thoughts about these issues? I do not know enough about the Masseys to argue. (My "vintage tractor" experience is mostly Allis-Chalmers, courtesy of my father-in-law's purchases of a D-15 and a D-17 years ago while we were farming with him, and the Ford 660 I now own.)
As far as my original question about the compression, I would say it passed with flying colors. The four cylinders were 130, 135, 135 and 135. The odd cylinder was less than 4% variance with the others, so it fell within your 10%, Jon. I was surprised that the other three were identical. Interestingly, while they were doing this testing, the starter went, so there is now a brand-new starter included -- without an increase in the asking price! (Of course, that does make it harder to negotiate price, but all-in-all, I think that I won't argue too much with a "free" new starter.)
I did come up with another item that I need to research. I noticed that the plug wires are in sequential order, i.e., a firing order of 1-2-3-4. That struck me as odd. I know the Ford 660 is 1-2-4-3, so I looked up the MF 65 gas (Continental G176) motor on TractorData to see what the order is supposed to be. But, no luck, as it is not listed there. I checked the TractorData listing for the MF 165, which appears to have a very similar engine. (I think I was told once that it was the same engine, with certain improvements, but I am not sure about that at all.) The firing order listed for the MF 165 is 1-3-4-2. That does not mean, of course, that this tractor is hooked up wrong, but it does make me wonder. I will have to see if I can track down that information somewhere.
Anyway, I appreciate all of the help and the suggestions.