Cleveland system or Matco..Got to replace O rings on pistons..
Shows how much builder documentation I have..
My hunch is your caliper came out of cavity 6 of mold K90.
Here is a photo of Cleveland 30-9 calipers. Ref the PN on the adhered label. Note mine have the same "AWB 16 ink stamp as yours, dunno what that means.
Is that the ID label seen peeling up in your photo?
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... What calipers does that new "O" ring fit?...
Here's another question, one that I've toyed with myself: should I replace the brake fluid I've had in this airplane (and every other airplane I've owned) for decades with the new higher-temperature 782 (MJL-PRE-83282) per the service letter 0047-R1?
How frequent are brake line fires.....?
There's no downside. Upside is a much higher flash point.