OK, here's another opinion. Lets first examine the lower bearing on a connecting rod. The crank pin rotates, thus providing a good film of oil to ride on. This film of oil will tend to cause the crank pin to ride somewhat near the center, if lubed properly.

The upper end, on the other hand, just pivots back and forth. If all castor is used, and the engine has been run very lean a lot, there may be a film of varnish covering the upper end. If the oil hole is clogged by varnish, it may be blocking adequate lube. To extreme, this can freeze the upper end of the conrod to the wrist pin and transfer wear to the piston to wrist pin bearing surface. BTW, this same effect can be caused by an engine just sitting for years until the upper end lube hardens or corrosion freezes the conrod to the wrist pin. For this reason, if you get an old engine it is a good idea to check that the upper conrod pivots freely on the wrist pin.

Just offering another possibility. If this was covered and I missed it, apologies.

George