Delta: Push Pop-Up with Overflow

I installed a Delta pop-up drain on a bathroom sink with no problems, so I purchased 2 more for my other 2 bathrooms with identical sinks. However, unlike the first the second leakes from both top nut holding the drain to the sink as well as the lower fitting down pipe. Also, when the domed cap in the sink is screwed tight the pop-up doesn't engage. If I loosen it a bit it engages, but doesn't release. To get if to work I have to unscrew it a complete turn and then it wobbles. I tried both new pop-ups and they are both the same. I even took the chrome cap and pop-up assembly from the good sink, but it didn't work in the second drain assembly. I can live with the loose cap and will now try plumbers tape to fix the leak.

I've been very happy with this drain for the first two years. Looks good and seems sturdy but now it won't pop open when I push. It's been getting worse for the last year and now it seems permanently stuck down. It disassembled it and cleaned out and greased up the internal mechanism to no avail. I believe that it is worn just enough to keep it from working.