Maybe one of the key tumbler pins got stuck.
How old is the vehicle?
nangyari na sa akin yan..bigla nalang nag stock up ung manibela..dun sa evengelista .pag pasok ko ng susi ayaw ng mapihit ng manibela..tumawag nalang ako ng gumagawa binaklas nila.tapos parang may binarena ayun umayos naman.kaso hindi na siya nag la lock..
instead of wd40, try contact cleaner. "it leaves no residue" that can harden again in the future.
(sounds like an ad, but i believe it.)