If any part "B" contaminates part "A" your part "A" will eventually get killed. All that is needed is time to render your part "A" useless.
Meanwhile the slight contamination of part "B" by soaked film and the "wetting" of the film by part "A" kinda "seasons the part "B." After about 20-25 rolls of film I notice that the mids in my film get more pronounced, and this is a good thing.
I have used Diafine extensively. One season I shot on average 150 rolls of film a month when Legacy Pro (rebranded Tri-X) was $2.89, and rebranded Acros short dated was available for $1.89 a roll.
Eventually Diafine got dark brown and was no longer amber, but still worked fine. The developers did get thicker and were more like a syrup, and I had to add an empty reel to the top due to foaming, but the developer still worked fine.
I mix a fresh gallon batch of Diafine about once a year. Also I tend to throw out the black sediment that settles at the bottom of the bottle. I suspect that the black sediment is accually silver. When basically I have exhausted the stock that I use to top off due to spillage, draining out the sediment... I remix up a fresh gallon.
Not sure what caused your curling though. I assume you got developed negatives.