GM water pump

[Clarence L.Snyder]

The only two things I can think of that could cause the seals to go out
of a water pump that quickly are :
a: faulty pump
b: inappropriate coolant.

Several bad pumps in a row is a stretch.
What are you using for coolant?

Lack of flow due to bad heater plumbing should NOT cause a pump to leak.
The pump should be good for over 20PSI, and the cap releases at 14?
Check the cap to be sure it DOES release - but usually hoses would be
compromised or header tanks would rupture if this was the case.

Anything other than a 50/50 ethylene glycol/water mix or a compatible
propoylene glycol mixture can cause seal failure. Pure water is not
acceptable - period.