So funny story..
Finished up the timing belt and water pump job on the LX. It was satisfying hearing the engine roar to life, confirming those timing marks were in fact lined up right.
The cooling system with filled with distilled water only, to test and give one final flush before adding Toyota Red. But after running the truck for a few minutes, I began to notice
lots of water dripping.

My satisfaction quickly turned to dread as I pondered the source of failure.
Did I mess up the water pump gasket during installation? I know I installed that very carefully and torqued everything to spec.
Maybe the Aisin kit I bought off Amazon was really some cheap Chinese knockoff?
I had a drink and took some time to think. Surely I was at fault somehow. After some deliberation I realized the mostly likely candidate was the FIPG gasket between the thermostat housing and water pump inlet.
Yup, sure enough, I had used the wrong Toyota sealant (00295-00103), and failed to use enough of it. Turns out the correct Toyota FIPG is 08826-00100, but at $60 I just picked up some Permatex locally instead.
After a more generous application of Permatex and allowing a full 24 hours to cure, the system is working properly.