Hey, nothing about Liquidol is a bummer (except that I can't buy it at the grocery store!)
I've learned as you have that it eventually begins to weaken. It can look like yellow-brown soup and still produce good prints - I've poured it into a tray and found mold growing in it even. So nowadays, it it's not a fresh batch, I drop a scrap of paper in the tray under room light and really check it out - in fact, my next print session with fresh liquidol, I'll do a max-black strip test with half-stop increments and keep it in an envelope on the wall, so I have a definite comparison. Do a quick scrap under room light, blow dry it off, compare to the strip test, so there should be no arbitrary idea of "is this black enough".
BTW, when you sense it's getting weak, you can finish your session by splashing a bit more concentrate in the tray - no need to dump it if it's not really really shot. Add a bit of concentrate and finish your session.
AND - save weakened liquidol in a separate bottle - it's a great toner! After you bleach a print, add to tired liquidol with extra water to make it half strength or weaker. With MGWT, it gives you a great warm tone, and will return highlights much better than variable toners. If you "print for toning" by adding more highlight density or a bit of flash/fog, very dilute liquidol next to a tray of stop bath will allow you complete control of highlight development. For 2nd pass lith prints, I often go to completion in lith, rinse the paper very very well, and then get the rest of the highs back with dilute Liquidol. Excellent combination, though liquidol can impart its own color in those cases - test test test.