Agreed, you should take the left clamshell apart and shoot down the internal parts with electronic spray. Doesn't take long, 20 min max. You don't have to go to a computer store nowadays for electronic spray. Cheaper at Lowes, Home Depot. Even Walmart might sell them. To get the general idea, Youtube video
here. Note: the author neglects to completely remove the movable contacts and only dabs on dielectric grease.
The reason for taking the left clamshell apart is the movable contacts can get quite encrusted. There's tiny coil springs under the contacts. Make sure to clean out the slots for the legs of the contacts too (right pic).

To get to the movable contacts, remove the thumb lever mounting plate. It's not absolutely necessary to unscrew the thumb lever from its mounting plate but some people do.

Then pluck out Holder B from it's notch and separate the stationary contact plate from the movable contact cube.

