Can you share a brand/part number with us ? Also, have you measured the pump pressure to assure that it's in spec (4 - 6 lbs) ?
I've been able to buy brand new pumps for my '55 engines (3 of them) from CarQuest.
They were identical to my originals except for the absence of LOGOs that were on originals. The new ones had no identification marks. All 3 have been in use for more than 5 years without any trouble. From curiosity I took one apart a few months ago just to see if the soft parts were being affected by junky gas. NO PROBLEMS. It still looked new inside. If I recall correctly they were priced at about 40 dollars each. Surely they would also have them for the newer and more common engines.
Marshall Goodknight C300 driven daily