I have a batch of Microdol-X I hadn't used in a couple of months. Then the other day when I developed a couple of rolls of 120 Delta100 in it I noticed the grain is a lot more pronounced than usual... Actually looked pretty neat and has a nice texture to it. But not what I normally get with fresh developer. Is it the developer, or did I do something else silly? After Microdol-X 1:1 12min 68F, with per-minute agitation, I give the film a 30 sec rinse in tap water, and then 4 min in TF-3 fix. After that a rinse in tap water and final rinse in filtered water with a little PhotoFlo. Same as perhaps another 50 rolls before it.
I love Microdol and have been using it since 1972. It's got the finest grain I have ever seen with the TMax films as compared to what i got with Tri-X or Pl-X in the old days. Film has gotten so much better in that respect. I also find I hve more control over my compensated development times. Although contrast is a bit low I don't mind since i make that up in paper grade.
I do find old developer doesn't work well if stored too long, 3 or more months. Perhaps you should buy smaller packages to make a quart so you won't have to store it. OR the other alternative is shoot more film. You'll get more consistant results using fresh stuff. How is your fixer, maybe your problem is not developer but instead a clearing problem?
The film should not see more than a 4degree temperature change from solution to solution either. - I mix my own. Microdol is:
750 ml water
100g sodium sulfite
30g sodium chloride
water to make 1 liter.
Capacity is 4 8x10 at normal times - 2 8x10 at 5% and 2 8x10 at 10%
rate your film down 1/2 stop or so.
1 roll is about 1 8x10
cut the batch in half and cut the capacity in half - now you can streach it over more months.
I had the same thing happen on a roll of 35mm tri-x developed in Microdol X that was a few months old. Instead of the usual fine grain, the grain was really noticeable. Contrast and overall tonality was fine.