The problem with contact cleaner is that it won't remove the dirt, dust and oxidation.
It will losen the oxidation and allow the dirt and dust to shift around a bit.
In the best of cases the contact cleaner will evaporate completely (leaving the dirt where it just happens to sit now) but in
the majority of cases this doesn't happen and the contact cleaner have only added to the mess.
The result is often fine at first but come back a week later and the problem has returned.
For most things, like f.e. potentiometers, I like to take them apart, add contact cleaner and
then wipe clean, dry and put back together.
Having said that, there are places that are very difficult to get into, like f.e. the front row of switches
of the Beomaster 3000/4000/4400 series. Here I usually place the Beomaster face down on a towel or similar
and spray contact cleaner in from behind.
Let it flow through the switches and drip out the front, excersizing the switches all the way as you go back and forth.
Let it soak for a couple of minutes and then flush and excersize again
This will flush a lot of the mess out and the results are usually fine.
If you doubt a speaker switch, you can bypass it momentarily for a test but make sure you don't short an
amplifier output.
Martin