I am amazed by how well my UC18 is tracking now that I replaced the broken plastic gear.

Makes me wonder how long it had been at least partially damaged.

I figured out that it is so important not to over tighten (stress out) the set screws through the plastic part onto the steel shaft.? Just snug rather than "tight".

My idea is that I damaged the part by not being careful with my accessories under the VMB and allowed an interference to occur.

I have reorganized my accessories to prevent any chance of interference to the path of the primary mirror as it travels over the rocker.

Here is M76 (a difficult target for me) from my UC18.