gasket to seal to the outside of the block. As long as it is torqued properly, it should not leak. Exactly where is it leaking?

The block is aluminum and a bolt could have been over torqued at some point causing one of the 20+ bolts to strip. It may be leaking from that area
since it can’t be torqued.

Note Toyota has a TSB that says there can be minor leaking from the weep hole at times and a very slight leak that drips once in while as long as your coolant level doesn’t really change, is normal. You can’t really see the weap hole as the fan pulley is in the way. You can see it with a mirror though.

Maybe they aren’t replacing the 2 o-rings properly or cleaning the mating surface of the block completely before installing the water pump gasket. The block could also be scratched from the previous replacement so the gasket doesn’t seal. They should also be putting a sealant on the larger bolts threads.

Maybe you have just had bad luck but Aisin is one of the top Toyota parts suppliers.