Here’s some follow up photographs.
The original problem at 185C photo shows holes. Found the missing areas were totally synchronized with knurled nut rotation (in photo at the red mark) Removed the nut and examined it. The machining left some bits in grooves on bad area. The bits are one edge of the teeth folded back I think.
A good cleaning under 10x magnifier with exacto-knife knife and tightening the idler a lot has made it workable but not great finish.
It’s not a circular error or the surface would have a sinusoidal wave to it. Instead it’s a sawtooth. Filament thickness builds to max thickness then falls instantly to min thick. Probably right at the bad teeth on knurled nut.
