Did two rolls of Tri-X 135 yesterday in well-aged Diafine. Both came out well at ISO 1250. Some shadow detail is not as good as I get with D-23 1:3 at 400, but I expected that. The Diafine negs scan very well and produce good wet prints. I don't use it much, but it seems to last forever. I jus top both solutions up and put it away until next time.
B&H lists Diafine in the quart size but they won't ship it. Adorama has it as well and, apparently, will ship it.
My favorite combination with Diafine is Eastman Double-X rated at 650. It has the property of boosting contrast on an overcast day without blowing the highlights when shooting in bright sunlight. It's pretty much the only film that I use now for 35 mm.