I typically do one section at a time starting with the front end. The push button boards on the SX series are difficult to access. They are tucked up under the tone and selection switches and they sit in a recessed channel. You can see the wire harness and the "step" in the chassis in this photo. This prevents the boards form sliding back (to clear the face). You have to "unpack" the wires from plastic clips and snip any cable ties. Once the wires are clear the board can tilt down at the rear.
However, some of the wires wrapped to the switch board can be so short they still prevent enough movement to clear the board from face. In this case the wire will need to be removed and replaced when re-assembled. I had three wires on this unit that I snipped lose to get the switches out.
All the switches and pots are treated with DeOxit. New audio grade capacitors are installed and the boards are cleaned... front and back.
Below, the switch boards are out. These are cool switches because the top comes off. They are held on by a set of clips that can be removed. This allow complete access to the contacts inside. BE CAREFUL!!! Once the top is off, the switch can come completely apart! Don't press the button without placing your finger over the rear to hold it onto the rails in the body. Also, don't bump or lift the front shaft of the switch, as it will cause the rear to lift up off the rails.
Once the switch is apart you can place deoxit (or your favorite switch cleaner) directly onto the rails and contacts. Be careful... be careful... be careful!!! Excessive forces form spray cans and bottle applicators can lift the switch from the rails. Place gentile finger press on the switch to keep it seated.