Most bearing failures are due to over tightened belts, followed by miss-aligned pulleys. Looking at your picture you has a corrosion/cavitation problem, you need to very aggressively flush the cooling system out, even get a sacrificial anode.  Skeptic is giving you some good advice. Bearing wear (& impeller shaft getting into the housing) is 99% a belt issue. CORROSION (and/or cavitation erosion) is a function of the overall cooling system design & the coolant you're using. FYI-I've laboratory tested Royal Purple's Purple Ice and when used as directed (may need more than one bottle with deionized water) it does a good job at preventing corrosion (fyi-my company used to make Purple Ice for Royal Purple).
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
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