I've had to throw old presta adapters away, that had just got to where they wouldn't work any more. There is a rubber ring inside the bottom of the adapter - I believe that mine had rotted from my leaving it on the valve stem, out in the weather. Leaking around the seal, making it harder and harder to make it work. A new adapter lives in my saddle bag now and that problem has not recurred.

They're cheap, I use them frequently, they work fine. Just get a new one or two, and if that doesn't help toss the tubes. Life is too short to make a project out of it.