The procedure we use for cleaning (when we can't do a disassembly and ultrasonic cleaning) is to flush with carb cleaner spray, work the key in and out, and repeat several times.  After the cleaner has evaporated, we use a specialty lock lubricant, but have had great luck with Tri-Flow.  It was reallly the standard until this synthetic lock lube was introduces by Briggs and Stratton several years ago.  If you can't find Tri-Flow, Mobil 1 or other synthetic motor oils seem to work well, too.  Do not use graphite or WD40...they'll cause you problems down the line.  Most of the sticking locks we encounter are loaded with graphite, which combines with the heavy grease VW used and turns to cement.
Steve