I doubt it's oil content related.

From the 170 onwards, all my engines are cdi and I've always used 10% oil. If it was oil %, I would have had more than the 2 failures.

If anything, I would say it may be that the bearing was a bit tight? But that's only a theory.

Previously, I've run a couple of tanks through on the test stand. Now I give the engine a really good break in with the break in needle open. I run at least 2 litres through at a very rich setting on the test stand, then close the break in needle and fly it.

It would be interesting to know what factory clearance should be, but not much chance of finding that out. Lol.