All the stuff I am reading online points to contaminated coolant being top of the list. You can’t really overtighten the belt since it’s self adjusting with timing belt…..and the gasket is pretty easy to work with. I did replace the o-ring on the pipe that goes to the back of motor. Plus, no leaks at all down there for 1500 miles. Then boom, it starts leaking. Last pump was seized when I removed it in September 2021.
Glad to hear that you found the issue and it wasn't the water pump.
Aisin is the OEM manufacturer for Mitsu pumps, so it would be hard to blame the pump itself.
The timing belt aspect though is a good thing to note though--they can be (and often are) over tightened.
If you're doing it yourself, the goal is the find equilibrium with the hydraulic tensioner. if you over-tighten it and compress the hydraulic tensioner past the pinned height, you're adding more stress on to all of the components it runs.
A "perfectly tensioned" belt would be tightened to the point where you can remove the pin on the tensioner, crank the engine by hand several revolutions, then install the pin back in the tensioner. This would give you full travel on the tensioner for future belt stretch. That said, if the tensioner is a *tiny* bit extended, that's preferable to it being compressed. I've never seen hydraulic tensioners become fully extended if set correctly--the belt will typically snap well before it will stretch to that amount.