Yes, the inlet should be B. If you want to confirm, stamped in the body of the pump should be two arrows confirming the flow direction. In your photo just to the right of where B is and left of A, horizontally on the pipes molded into the pump body. Look more closely at these spots with better light.
These pumps are almost all identical and they're really cheap. I have two of these:
If you can spring the $60 for a replacement as a test, they're also really easy to replace because those fittings just thread on and off - you may even be able to do it by hand (they're washer-sealed so you don't need / want to torque them down like mad with a wrench - you'll crack the plastic fittings.)
They're also useful even if they leak. I kept my old pump when something similar happened and added a switch, 20' of wire, and a bullet/SAE style power connector. I put the mating connector with an inline fuse on my battery bank in my garage. Then I got an "Aquatank" bladder (also cheap on Amazon). I can fill this at home or at a camp site water station and use the pump plus a cut up garden hose to fill my fresh tank when we're at sites like BLM land or state parks where they have no water at the site.
