Right channel issue TU8600 anyone have a copy of the manual?

I’ve had this amp for about 5 or 6 years and it’s been mostly good. For the past year or so I get a weird right channel where it sounds quiet but distorted. Or it’s just super quiet. I swapped tubes and it’s still the same channel. Problem was occasional. Now it seems to be getting worse.

I’m about to pull it out and run through the testing again but I no longer have the assembly manual. Anyone have a copy?

Also welcome any ideas on how best to troubleshoot.
 
Finally got around to doing this
 

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I tested the amp and it checks out (voltages). The problem goes away when I move the tubes around so either the sockets are bad or need to be reflowed - which I already did and it came back. Or maybe the tubes are just getting old. Honestly I don’t know.

For now there’s no problem. I’ll eventually get new tubes and try to chase it down but right now my laundry list of **** to do is long and this isn’t at the top