i have the Shimano STI brake / shifters and they gum up and don't shift anymore. i took it to my LBS for other work too and it was fine for a couple months. Gummed up again and i took it back and they fixed again and told me the fix is WD40.

So they're gummed up again and i want to do it myself. I sprayed all over, made a mess and only freed up one shifter -sort of.
Where do you spray? do you squeeze the brake and spray from the top? or through the hole on the side? Do you drain the can or just a few blasts?

How long should this fix last? are they shot? they get very little use - 20 miles a week through the warm months