In no particular order:

-The thing about capacitor discharge is that you can have too much of a good thing. All amps have some 'bleed' resistors installed across the caps to drain off the charge. If these were selected to drain the caps quickly, the result would be just like a 'leaky' cap that doesn't hold charge. The unknown part is how long it takes to get down to a safe level. I use a big wirewound 10 kOhm resistor all bundled up with insulation, and a voltmeter. Be very sure there is no stored voltage lurking about before you go poking around in the cab with wet cloths!

-A good glass cleaner should work on the tubes. Be gentle about it.

-Unfortunately, the wood inside amp cabinets is rarely sealed properly, allowing stuff like mould to root deeply. Be persistent.