Maybe it is not the pump at all. There is a Pressure Discharge Valve on the Nordson pump that can fail and cause the pump to stroke improperly.
Don't spend the big dollars on repairing or replacing the pump until you have verified that the Pressure Discharge Valve is working properly. The Valve is $225.00 vs. over $2000 for a new pump or $995 for a rebuilt pump.
If this is not the issue, please call us at 800-235-8090. We will assist you in troubleshooting for free.