Before you go spending money on a new pump. Pull the old one out. If it has a leather cup just oil that up good. The proper oil is Neats Foot Oil but I just use 3 in 1 or sewing machine oit. Soak up the leather good the spead out the leather a bit. Check inside the pump bore for things that are not suppose to be there. If the check valve shut off rod is still there it is usually easier to take it out and put it in the pump shaft then install the whole assembly. I have yet to replace any leather pump cup. Now if you have the neoprene cup, probably have to replace it. In my Opinion.
Randy