For what it's worth, old lock grease tends to move away from where it's needed and turn into a hard, waxy substance. It's arguably better to have a lock cleane

For what it's worth, old lock grease tends to move away from where it's needed and turn into a hard, waxy substance. It's arguably better to have a lock cleaned and slightly lubricated with WD-40 than one gummed up with ancient grease and dirt, or worse, rusted. I've heard a lot of anecdotes in every direction: only use graphite, only use a cleaning solvent. I've never read anything authoritative and I suspect the ideal approach is to regularly (e.g. every decade) disassemble the lock, clean it thoroughly, and inject grease, but nobody is going to do that.