[Arran]

I suspect it's more of a bias issue, that is assuming that the usual step of replacing the paper caps has been taken, whilst I am recapping a radio I always check the resistors as well, many overlook this step because the internet tells them that caps fix everything. I have never had an output transformer partially fail, they either have continuity, or they do not. Part 16, likely an electrolytic capacitor should be replaced, as should part #15, the tone correction cap across the output transformer primary. The resistors parts #24 and #25 should also be checked, actually I would check all of them, if any are more then 20% out, replace. If you also have a spare 1H5 tube, I would substitute another, but I suspect a bias issue in the audio output stages.
Regards
Arran