I've got a little more than a half gallon of XTOL and about a half gallon of TMAX RS that are both just about three months old. Should I toss this and mix some new developer, or is there a way to compensate for the age? Thanks.
If the dilution is more than 1:1, discard it. If not, go ahead with the clip test. That said, it would hurt more if you ruin the film running it though an exhausted developer.
All the best.
One note of caution, XTOL can go off very quickly, with no color change. Since it has been mixed for some time, it is best to test every time before you use it.