Thanks for the link! I didn't have version 3 of that TSB. 
There's a date code (2-digit year) cast into the Hitachi cylinder head, shown below. Mine was original from 2010, replacement produced circa 2019. Not sure if the 6-digit number on the end plate is also a date code. Mine was still intermittent, would work ok most of the time, and sometimes give the fault C1A20-64(6C), "Pressure too slow filling.". But the fault was occurring more often, and I wanted to get it fixed before catastrophic failure.
I still think I might have a small leak somewhere but so far, the fault hasn't returned.
There's a date code (2-digit year) cast into the Hitachi cylinder head, shown below. Mine was original from 2010, replacement produced circa 2019. Not sure if the 6-digit number on the end plate is also a date code. Mine was still intermittent, would work ok most of the time, and sometimes give the fault C1A20-64(6C), "Pressure too slow filling.". But the fault was occurring more often, and I wanted to get it fixed before catastrophic failure.
I still think I might have a small leak somewhere but so far, the fault hasn't returned.
