Over the years and after many, many extensions and retractions, the big left side slide has crept forward. The slide has moved forward enough so that the difference between the clearances on the front...
I had the same issue on mine, it was so bad it was rubbing and killed the slide gasket. My slide sits on 3 pads that connect it to the slide frame and where these pads connect to the slide the bolt holes are slotted. We simply jacked the slide up using a car jack and a 2 by 4 until it cleared the pads, then with 2 guys pushing it slid back about an inch. I tightened the bolts on the pads and it's done...