I had been considering the Italian made Bolex 521, but I now discover that it can suffer with worm trouble. Furthermore, Bolex do not stock any such replacements.

Does anyone know exactly what the problem is? Would I be wise to pass on this projector?

Hi Maurice,
I know nothing of the Bolex machines, but if they have a reputation for worm gear troubles, I personally would avoid them. The Bell and Howell 16mm machines from the 70's and 80's are NOTORIOUS for worm gear troubles. Specifically, the material that they were constructed of (some variation of nylon or plastic), develops large cracks over time, even if the machine has not been used very much. They can't be repaired, only replaced. Some collectors have been successful in replacing them on their own, or have paid out big money to have them replaced. But that's only my personal opinion. Best wishes in whatever you decide. :-)

If anyone ever needs a specific worm or spur gear etc etc, manufacturing from Brass, Steel or any other such like material, let me know.
The guy who manufactures the new spindle hubs for me, can easily manufacture other such components at a competitive price for one off engineering work.

For an otherwise beloved machine, it is well worth the outlay imho.

Plastic gears and the likes, were never really designed to stand the test of time for machines reaching 30, 40, 50 or even longer years of reliable service.

Hi Maurice, here the link from Bolex Switzerland.
https://www.bolex.ch/NEW/index.php