I noticed a fall-off of the lith effect with the LD20 after about four months. Prints still developed and I got the same colors, but no infectious development. Perhaps the sulfite/bromide balance was not right for the paper, but I was pulling my hair out over it. That's when I actually read the materials, and it says 60 days. I still have a few liters, maybe from what you say I should give it another go and play with the chems a little more.