Checked the breather and it looks like new. I pressurized the gas tank and got it running only to have an abundance of smoke coming out the muffler. Next I noticed oil dripping from the
pipe coming out of the muffler. It smoked profusely before it had the rings and bearings replaced. Going to have the mechanic take it apart again. Guessing maybe valve guide???
I would run engine WOT for 30 minutes to smoke away all old oil slobber from time before rebuild. New rings need seating new rings don't contact completely around there circle highs need wear off so complete contact. Opposed piston engine over lube piston rings at rebuild take sometime to burn away oil because oil in bottom part combustion chamber as much as 1/4 teaspoon burn away slow. Valve guides on opposed engine upper part crankcase oil amount that bypass guide after warm up be next to impossible to see a smoke from engine. Lappet oil wiper spring not butted ends would give smoke after warm up.
Run engine for 30 minutes see if smoking goes away.