[R-390] Carrier meter

[Gordon]

I have noticed that my Carrier meter doesn't consistently go to Zero. 
The Meter itself seems fine.
I turn the RF gain fully counter-clockwise, adjust the carrier meter pot 
on the IF module to zero it.
all is fine, but the next time I turn the radio on, it is no longer at 
Zero. I have cleaned the pot, but that doesn't seem to be the problem.
Is this a known issue that I do not know about ?  LOL
I replaced V506 thinking that might do it, but still the same.
Can anyone shed some hints ?

Thanks,
Gordon
N6WK