Showerthought: I cleaned lens threads with the wrong brush for 18 years

I was cleaning a customer's 50mm Summicron last Tuesday at my bench and grabbed my usual old toothbrush to sweep the filter threads. The lens was back in for the third time for the same gritty focus feel, and the guy finally asked if I was using anything abrasive on the threads. That question made me stop and look at what I was actually doing. Turns out those stiff bristles were slowly grinding grit deeper into the aluminum threads instead of lifting it out. Now I use a soft camel hair brush and a squeeze blower, and the last 12 lenses I did have come back clean. So which side are you on, do stiff brushes actually clean better or are we all just wearing down threads faster? Tell me what you use on filter threads and if you ever had a come to Jesus moment like this.