The issue is probably the rubber wipers on the side of the trailer that are supposed to be flexible enough to twist out when extending the slide and turn in when retracting. They have become hard and will not twist in and therefore become wedges against the retracting slide. A short term fix is to put baby powder all over the side wall of the slide as the slide retracts. The microscopic powder granules will lubricate the rubber against the slide.
Another option is to flood the rubber and sidewalls with 3303 protectant.
