New Variac for Joule Electra Amps

I have a pair of Joule Electra VZN-160 amps and have been using them happily for the last six years. They use a single outboard variac for voltage regulation. I how have a problem where something inside (the core) is glowing and a burning smell starts to manifest.

I'm able to send it in to their out-of-warranty repair facility for a likely core replacement (likely $500ish or more) though it will take ten weeks before it ships back.

Has anyone got other ideas on how to fix this issue? Is there any after-market variac that would work, or could I just somehow get a new one?

Thanks in advance for any suggestions.