Hi John,
The tumblers on my LJ are 14DP in steel or cast iron (CI I expect).
I am currently making some for another LJ in acetal and aluminium. Plastic gears are meant to break before the other gears, I suppose. I think the lead screw is protected with a brass shear pin, but the power feed shaft likely needs a weak drive link fitting somewhere in the gear train.
It is worth setting up for gear cutting as a couple of replacement gears would likely pay for an involute cutter and arbor. Easier if you have a rotary table. I have a set of DP16 and a couple DP12 cutters but am now looking for a set of DP14 cutters, now I have a 5"
It might be worth asking on the yahoo and freeforums raglan machines fora?