Thanks,
I did another foil test last night and I do think this unit is
probably working properly. I saw about 20-30 small perforations form
over a 10 minute cleaning cycle. Maybe I missed them the first time
because they are very tiny. Once I hold the foil to a bright light
they become obvious.

The transducer ohms out as infinity and looks solidly attached to the
tank and I see no cracks or other damage.

I'll take another look tonight but I don't recall seeing any tuning
adjustment on the circuit board.