if your dealer fixed the air leak ( sounds like that was the problem) and had not changed the carburator settings, (because it did cut okay until it ran lean before any attempt at a fix), then it should have run okay after bearings and seals were replaced. I'm wondering if he even took it apart to install the new seals/bearings but simply played with the carburator settings hoping to cover it up enough to get by. Just guessing because it sounds like your dealer comes up with a lot of strange excuses. I think your only recourse is to keep pestering Makita.