Yup I'm aware of that - no good tech would diagnose a system based on pressures alone.
For a refrigerant leak: deteriorating performance over time, oil at the site of the leak (you won't spot this if the leak is inaccessible), high operating costs.
I really think first tech misguided me and wanted to sell new system. 2nd Tech did replace valve on the HOT side of the pipe. My machine is working great since the repair (30 hours).
Is there any sign I should look for?
I've discovered a natural law - everything gets progressively worse. Things only break down and become depleted. Life isn't worth living and everything is going to hell.
Death is the messiah. Everything else is irrelevant and arbitrary.