Was it slow and labored before you changed the fluids?
As far as being normal a lot of these old tractors do that. It doesn't mean it is right.
As for worrying about it I doubt the tractor will dissolve.
Allis Chalmers, Stated in the manual the oil used must not foam. The local dealer said do not use detergent oil. I understand detergent oil holds the dirt particles in suspension. The hydraulic system on a WD does not have a filter, that is why I do not use detergent oil in my WD's hydraulics plus the fact I wonder what it does to the seals.
I agree modern day hydraulic oil is better than what they had back in the day but I still use a straight weight non detergent oil for the hydraulic on my WD.
In my opinion the fact that over the years a lot of farmerts did or did not do what the manufacture recomended speasks well these old tractors.