to the best of my knowledge the water pump only has two items that can deteriorate: the seal and the bearing.
A worn bearing would be evidenced by excessive play in the shaft (perhaps see shop manual for details). A bad seal will allow leakage out the seap hole on the bottom side of the pump.
You can get your current one rebuilt for $80 and get a year warranty (Arthur Gould in NY). They glass bead it so you can paint it nicely, as well.
6 blade fan is a +++.