We have about eight Schlage Regent Leverset internal door handles in our house. One started squeaking when it was about ten years old, I had it replaced, which also squeaked. Since then it's been replaced again, and I've had Exceed have a look at it as well. Exceed fixed things up a bit and sprayed some CRC into the mechanism. It was quiet for perhaps a month or two, after that it didn't squeak but it started feeling like there was sand in the mechanism.

I took the door handle apart again and some black dust fell out. The only think I can see that's black looks like a spring. I sprayed it with CRC, put it back together, and it works smoothly again. Last time this was done it lasted a month or two until it felt graunchy again. The smell of CRC lingers for a week or so, which is unpleasant.

What's confusing me is why six door handles have worked for 12 years or more with no lubricant, but one new needs lubricating regularly, and one of the older ones is going that way.

Can anyone suggest a lubricant that lasts longer and ideally has very little smell? Or is there something way to approach this.