I had the same problem the only thing that worked was silicone grease, on your finger and under the seal. Don't confuse plumbers silcone gease with silicone sealer. I went to Lowes and asked for it they tried to sell me silicone sealant the stuff in a tube that would have been some mistake. I got it at Ace Hardware its in a small jar with a screw on cap.
07 Itasca Ellipse 40fd, 2014 Honda CRV, greyhound lab mix, pit pointer mix, stupid cat, wife