[Eliot Ness]

I might be beating a dead horse here, and you might have tried all of these suggestions, and if so, just ignore.

The most useful initial test is to break the radio down into sections and completely rule out sections. It sounds like you've done that (at least with the audio section) if the Bluetooth never cuts out.

I have seen bad solder joints that looked good on the surface but were just bad or cold joints that somehow got covered with shiny solder. I think you've done enough tube substituting to rule the tubes out, but the tube sockets and all solder joints could be suspect so you might want to systematically start resoldering all joints in the suspect section/s. At this point I'd replace ANY original resistor or capacitor that remains (even if they initially measured OK), especially before the audio section. I'd also seriously consider replacing the sockets of suspected tubes.

I’d also replace that complete candohm if you haven’t already. They are known to intermittently ground to chassis. It looks that it’s just a three-section resistor easily replaced with a terminal strip.

And on my schematic of the 6S254AT (turntable version) C5 and 14 are listed as .1, so you’re OK with those values… I have a parts chassis for the 9 tube ‘38 but not the 6 tube. Fortunately it's a nice roomy chassis to work on, although by now I’m sure you’re sick of looking at the underside!