Second, there is a wad of felt in the glass tube inside the
handpiece that also becomes saturated with fine solder dust and flux. I
have not found those to be recoverable due to the non-soluble dust. I got
a bag of them with the machine, so I'm
probably set for life.

If they are anything like the felt wads fitted in the same place in my
Weller vacuum desoldering station, you can recover them once, sometimes
twice, by just running a curved, blunt scalpel blade over the surface as a
scraper. The surface layer thats stuffed with solder dust, just falls away
re-exposing clean, uncontaminated felt. I would guess that you perhaps lose
a half a mm from the pad's thickness.

Arfa