No32 replacement advice

[Surpmil]

A shop that repairs instruments such as theodolites should be able to handle this no problem at all; particularly if you provide them the drawings from Peter's book(s).

The turret assembly/block is brass so you might try playing a hair drier over that portion and warming it up a bit in case lubricants have gone hard? Would take a while for the heat to migrate through the 1/2" or so of metal so patience will be needed.

After that perhaps the gentle taps with soft-faced hammer as Warren suggested; and he meant only on the rough-cast areas of the turret, not the drums!