What is needed:
Piece of plate, take broken screw assembly out of lube size, find the center of the hole inside the lube sizer and mark on plate, also mark your two hold down centers.
Drill 1/2" hole which is the outside dimension of your the round head on the screw assembly in the plate, do not drill all the way through, what you are doing is allowing this to spin inside the new base plate when done.
Then drill with 1" bit to ream the hole out in the base plate to the size of a 3/8" washer outside dimension, which you are going to slide over your screw assembly.
Also drill your two hold down bolt holes.
To assemble, make sure the threaded assembly with washer fits freely in the new base plate with your hand (do not have the threaded upper piece in your lube sizer at this time, just checking if you drilled everything deep enough).
Assemble the screw assembly with 3/8" washer, push it from the bottom of your lube sizer up into lube sizer, install one round rubber O-ring which fits over the outside of washer and has more height than washer, I put a little grease/oil on these parts as they will turn (washer and head of threaded screw assembly), bolt down the o-ring provides a seal between the base plate and the original lube sizer. It works great for me. It turns as easy as before, the only thing is your upper threads are about an 1/8" to 3/16" lower but you can still start the threads to bring the upper assembly down with wrench (I start mine out with a battery drill after I get it started, it's much faster than the ratchet wrench.)