Installing axel seals

Im over at a friends helping him install front axel seals on his 250. Passenger side popped right in but the drivers side will not go in even. Right now we have a piece of all thread rigged up with one large washer pulling on the seal and the other side it pushing on the outside of the axel tube. We tighten a nut to pull the seal in but it always gets hung up at the top. We have cleaned it and even sanded it but it will not go in.