Hi Dionne,
I have exactly the same beauties and use them very often apart from my handheld meters
Please try to rinse carefully all the switches with some mild contact cleaner first.
My proposal would be to remove the board from the housing and place the board/switches upside down to some kitchen roll paper and rinse the switches from the backside to front.
After that you should operate all switches a few times and repeat the cleaning process again.
I have good experiences with "Kontact 600" from CRC
Cheers
Arne