I had previously reglued my cracked water pump with superglue, and it was still spraying water out of this area while pumping.
Initially I thought I was trying to repair the pump just for fun — and I still mostly am. But when I window-shopped for replacement pumps and found them in the $70-150 price range, I thought I might try a little harder to fix it, especially since I’ll want a bigger pump when I install a shower but I’m not ready to figure it out and shop for it yet.
The plastic collar that bolts to the motor should stay dry during normal operation — a rubber gasket press-fits between that piece and the three-dome-shaped housing where the water flows.
I had superglued that horizontal crack (which is vertical in the previous picture), but it’s still (or again) open. For repair attempt #2, I scraped off the superglue, then undercut a groove along the crack below the lip, to have more room and surface area for RTV to take hold.
There’s actually about as much RTV behind the edge as there is in front, and it seems to hold pretty well. The mating edge of the rubber gasket is chamfered, so the RTV here doesn’t interfere with the gasket.
Cured, reassembled, and reinstalled, the leak has been slowed from a spray to a dribble. Seems like it’s worth another cleaning and seal attempt to see if I can catch the last bit of leak.