Leaky Sta Rite pump

I own an older Sta Rite Max-E-Glas 2 pump. It started to leak below the metal band that joins both halves. I’m wondering if I can just replace the large O ring where the two havles are joined, or if I need to replace the shaft seals too.

For that series pump, leaking under the band usually is a sign that the o ring there is either bad or needs to be lubricated. I would suggest taking the band off, cleaning the o ring and area where it sits, lubricating the o ring then putting the pump back together. If that does not resolve the leak then inspect the plates for any cracks. Usually, the shaft seal will leak behind the rear plate closer to the motor.