There's not much I can add that hasn't been discussed before in this forum about this carburetor. My 2 cents.
I have seen that the power-piston well can be worn to a slight taper, some wells have ridges, some wells were pitted and some wells were scratched by containments. The lower and upper edges of the power piston (annular rings?) can wear a little but form a sharp edge like a honed knife (you can feel the edge with fingers). After cleaning and fine polishing sometimes the piston moves freely again but I suspect this is a short term solution. The only way to find out is to run the rebuild on an engine. My take on a well working carburetor is that the piston-well wall needs to be straight and smooth and the power-piston to be at the original diameter. I doubt there is an economical way to bore, bush and hone the well and turn a new piston. The better alternative is to find a carburetor that has less wear.
