Zieg Warheit

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. The membrane part of the keyboard, where the contacts for the keys is printed on, is prone to deterioration. 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.