The weep hole is called a "tell-tale".  It leaks when the bearings in the
pump go bad and start to allow the shaft to go eccentric even a little.  This
kills the seal and lets the coolant start to leak out of the weep hole.  This
is important because if you let the pump go and then it totally locks up
(catastrophic failure) you could cook your motor and break belts which can
wipe out dip stick tube, etc.  The pumps I have are dealer pumps.  Perhaps
the last one you put in was inferior quality?

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242