Originally Posted By: djb
Most automotive locks are hardened steel wafers sliding in a hardened steel keyway. They are lubed with waterproof grease. This is unlike many padlocks and home locks, which have ungreased brass parts sliding against steel. These can be usefully lubricated with graphite.
Putting graphite in a greased lock will gum it up.
Since everybody else is necroposting...
What you say may be true regarding hardened steel wafers/keyways, but I have never had an issue 'gumming up' a lock with Lock Ease - a graphited lubricant. Dribble a little on the key, give the tumblers a bit of the old in-out, wipe it off and you're done for a year.
Silicone spray has absolutely gummed up locks before. Also had issues with WD40. But no problems ever using Lock-Ease or just scribbling on the key with a pencil.