Tube amplifier bad caps

If you are convinced it is caps, the larger ones are the more likely candidates. However, you are going to have to remove the circuit board to get to them as there is likely a solder connection on the other side of the board.

That means moving and/or disconnecting other wires. That photo also shows pretty tight construction quarters so you will need to be very careful with your soldering. You wouldn't want to short a trace or heat damage a sensistive component.

There are also other factors that can cause problems. You could end up replacing caps and not fix the problem. The best advice is to get a service manual and trace through the circuitry with the appropriate test equipment and precisely locate the problem.

Professional shops may not work for free, but they should know what they are doing. Good luck if you decide to undertake this yourself.

Just a quick observation that bad caps don't necessarily have a visible external leak. I've seen plenty of way out-of-spec ones that appear physically fine.

Do you have a voltage meter? Do you have a schematic that indicates voltages at various test points? (Keep in mind that voltages in a tube amp are often in the 400 to 500 volt range, or even more.) The key is to start a logical testing process to run down the problem.

Cleaning switches is a good idea (and won't hurt anything) but there are a number of possible causes for the noise. A bad solder joint, a resistor damaged from overheating, a mechanical foil trace failure, a smaller signal cap - any of these or others could be the culprit.