A GMS does leak air through the bearing and around it.If you have taken a GMS apart you might have noticed the channel dug in the case from the front bearing to the carb.If you fill it with RTV it will fix the air leaking problem.I read about the fix in an article by Dave Gierke,and tried it.It worked good.
One GMS I have the bearing is so loose you could literally shake it off the crank and out of the case.The machining of GMS engines is pretty poor.