Just finished in frame overhaul of a 1967 4020. After a good deal of cranking, I determined the oil pump was back in 180 degrees off (on the wrong TDC). When draining the oil to drop the pan, there was maybe a half cup or so of water in the bottom of the pan.
After dropping the pan, I can't see any obvious sign of it leaking around the sleeves. There is still a waxy residue around them from the john deere o ring soap, also if an o ring was leaking I would expect it to be seeping at a weep hole, which it is not, and yes I cleaned them of any dirt plugs when it was apart. Could it be the head gasket? What else could it be?
The only other possible thing I can think of is the oil cooler, but it seems unlikely that it would suddenly fail at this time, as there was no water in it before. Or possibly residual water from when I power washed it, but I'm 90 percent sure it had a pinkish color, which the Fleet Charge coolant I used is.