Adam, the wheel bearings on the 86' 300E are definetely adjustable and not the sealed type. I have the same car. So take the wheel off, get the bearing cover off and see for your self. To adjust it you will need size 5 Allen key. However if the griding noise is coming from the bearing and you are sure about it, then as might as well change it. It is not expensive I beleive it is less then $50.00 but check the price here and see.

Alex