Water bypass valve pipe

I have had slow coolant loss for over a year since I bought the truck at 80k miles. Truck is a 2008 2.7 and its 94k miles now. Coolant loss about 2" inches on the reservoir tank after 600-1000k miles. I bought the water bypass valve pipe but haven't had a chance to replace it yet. I have done a few tests so far below.

My question is regarding the pressure coolant test. Even though no pressure was lost during the test, would a small leak somewhere still exist? Also for Tacoma of this year, is blown head gasket common? The shop charges $175 for labor to change the bypass valve but told me it won't fix my leak.

1) block test (radiator) - passed, done at home
2) Coolant pressure test - passed,done at home and also at the shop
3) oil on dipstick looks good.
4) no over heating
5) no white smoke from exhaust

Thanks for reading.
TT