I have a SWR Workingman's 160 Bass Amp that crackles when the knobs are turned. I've tried different instruments/cables to no avail. I emailed a repair guy with some photos of the external surface of the amp to ask if he repairs this model and he said seeing the corrosion on the outside that it's highly likely that it's corrosion on the inside causing the crackle.

I've taken the casing off today an the unit is surprisingly clean on the inside. However there are small orange looking patches on the solder and I'd like to know if this was a classed as corrosion?

Attempted to attach pics to no avail. I'd like to know if I should just st throw this in the bin & get a new amp? Any thoughts appreciated.
Thank you.