I'm not sure "exactly" what Supertib was referring to, but I took it as he was talking about the OWB ruining the shaft. In your case, he may be right about that.

The other place you might want to check is where the shaft comes through the inner backplate. Often there is a bronze bushing there. If either the bushing or shaft wears at that point, excess fuel can leak out and cause the OWB to slip, even if it's good.

It's possible the backplate is an issue, so I'd check carefully, or you could wind up with quite a bit of $$$ spent on this engine, and possibly some of it needlessly.