[bwdz]

My first recommendation is to find a new mechanic. Anyone who just guesses valve seat and says that without doing any sort of tests should not have the word mechanic associated with them, more like a hack. There are many different tests for finding the source of a noise or a tick in the engine such as cylinder cutout tests etc... A qualified mechanic will diagnose those before blurting out some complete guess that involves an engine teardown. I can tell you how to perform these tests but since you go to a shop for your work I will be just wasting my breath as a qualified technician already knows all these.