The seller did get back, but I think the valves are actually OK. Pretty sure it was just distortion in some Maurizio Belladonna source material that led me to the conclusion. Cross comparing with other valves and they all present the persistent sound in the track with the same odd sounding distortion.

It's a bit like listening to Etherwood by Etherwood. There's distortion running through that, too, and if your not aware it is present in the source, you question your kit.