I've used Moglice 1000 (the Teflon-based epoxy) to cast leadscrew nuts when I had my Mill/Drill. It wasn't that difficult: I drilled-out the old nuts, sprayed epoxy release agent (that comes with the Moglice kit) on the screw, and made a set of dams for the ends of the nut (to keep the epoxy in). I drilled three holes along the length of the old nut to inject the Moglice.
Each coating of release agent will give you around .001" clearance when you release the Moglice nut. I think I used 3 coats (3 thou clearance). If the custom-formed nut is too tight, Moglice recommends using Bon Ami scouring powder as a non-embedding lapping compound to lap the nut to the leadscrew.
The end result is an extremely low-friction, and low backlash, nut.
For an old leadscrew, you'll want to re-cut the worn leadscrew to normalize the thread pitch, since the leadscrew will have much more wear in the center than on the ends. In the Home Shop Machinist article, the author re-cut the acme threads all the way down to V-threads, but that should only be necessary if you have a lot of wear.
Devitt Machinery (the US Moglice rep) has a page describing casting leadscrew nuts and quill housing too:
http://www.moglice.com/newsite/frames/wroteframe.html
If you Google "Sherline Moglice Nut" you can find several articles from a guy who cast near zero backlash Moglice nuts for his Sherline. The trade-off is that the tighter you cast the nuts (for less backlash) the more time you'll spend fitting and lapping the nuts.
Good luck,
Robert
