well i can see it being between the full and add sight glasses as being a good level but if it is in the 'add' sight glass then in my mind that means add fluid. AND... if the upper sight glass is the full mark then one would think to fill it to that level but not above.
And yes i know about JLG's engineers, they are a knarly bunch and no they do not like being questioned , in fact they can get right testy about it LoL...

any how... just draining out some of the oil so the level is lower than the 'full' mark (sight glass) should fix the problem.
:o)