You may have found the problem with Silicone. Not sure if it stays FIRM at all seal lines & joints when warmed up over 10 minutes & a re-wetting with fuel mix. The WOT vacumme & heat softening the crankcase seal lines may be the cause of leaning till a cool down occurs.

The more you describe the 10 minutes +- , the more it sounds to be heat related.

Can you afford a NEW wacker for about $60 ? I would pull this one & play with it on the bench. It should heat up quicker to make heat a problem.

No not tight fuel line ends ? Any old kinked spots? They will rekink when heated up. sometimes.

WHO said 2 strokes are MUCH simpler than 4 strokes?