[CalebD]

West system also sells the graphite powder to make a low friction surface.

I'd wipe a thin layer of vaseline on only the rudder shaft before pouring the epoxy; this will act as a mold release once the epoxy has set.
Use duct tape and some creativity to make the rest of your mold. Your mold will keep the epoxy where you want it to be - hopefully.
I'd bet that this is the easier option than using a machine shop and getting the dimensions right.