From my experience of disassembling and fixing several keyboards with fully or partially not working keys I can say that just cleaning contacts will not work.[br]
The membrane part of the keyboard, where the contacts for the keys is printed on, is prone to deterioration.[br]
Since the keyboard module is riveted to the top palm rest - the best chance to fix it, is to get a new keyboard assembly. It can be either salvaged from another base, or bought on ebay or aliexpress.