Trace Elliot GP12 Humming

[dpm309]

Working on a Trace Elliot GP12 250 SMX which has a noticeable hum. Replaced the 2 4700uf 63V filter caps and it reduced the hum somewhat. The owner wants me to replace the toroidal power transformer in order to reduce or eliminate the hum. Having a hard time finding a replacement except for British Audio who might have an old one laying around for $100 plus shipping. I don't think a replacement transformer will reduce the hum any further. From what I have found out on the internet is that it could be a shielding issue or the fact that the amp is almost 30 years old and some of the components are drifting or failing. Any other ideas? I had Doug upload the schematic to his schematic library.
Thanks

[PRR]

Which controls affect the hum?

[dpm309]

Both gain and volume controls affect the hum. It even hums on standby. The ground lift switch does very little to reduce the hum.

[shooter]

have you tried to jack in a signal at the FX returns?
does stereo/mono switch change anything?
you got one complicated pile o stuff in that amp 

[dpm309]

Tell me about it. I usually don't work on SS amps but am doing this for a friend. I don't have the amp right at the moment but will definitely try some more troubleshooting when I get it back. Also might try some shielding around the PT.

[PRR]

Both gain and volume controls affect the hum. It even hums on standby. The ground lift switch does very little to reduce the hum.

It has multiple issues. I hate to shotgun an amp but it may be time. It may be tedious as one hum-fix un-masks a next layer of hum.

I'd also ask for clarity: does it hum in the speaker or right from the chassis? Perhaps both, but as you re-cap the speaker hum you may come down to transformer hum.