Takes a special kind of pain to realize you've been fighting ghosts for four months. My buddy had a similar thing happen with his tool presetter, except it was off because he kept storing it right next to the coolant mister. Took him three weeks of chasing a .002 tolerance on some stainless before he cleaned the glass and got a good reading. Scrapping a third of a batch hurts, but at least you caught it before it got worse. Consider it a very expensive lesson in calibrating your gear more often. That .003 will haunt you more than any scrap report ever will.

Adam, you say the "paperwork stuff" is where it's at, and I get that, but I think you're missing why the wild stories catch on. Most folks don't have the patience or training to follow complex financial records, and shapeshifter tales tap into something more basic about fear and control. The boring truth is often harder to swallow than a good monster story, and that's a human thing that's been around a lot longer than tax forms.

Doesn't that risk damaging the O2 sensors downstream though?

Same here" is right, that's exactly what went through my head. I spent months fighting with a bearing bit on some oak cabinet doors and getting those annoying burn marks. Then a buddy walked me through using a pattern bit with a simple MDF template and it was like night and day, no more wobbling and no more tearout. The trick for me was making sure my template was clamped down super tight, otherwise the pattern bit would still wander a little. Once I got that sorted out I couldn't believe how much time I wasted on the old way.

That "stapled like Christmas lights" line hits hard, I've seen the exact same thing in older houses. Did a retrofit last week where the previous guy had zip-tied everything to the plumbing like he was decorating for a holiday party, completely impossible to trace. I just leave the old stuff in the joists if it's not causing issues, run the new coax along a different path through the attic instead.