I used to use dry graphite sparingly until my locksmith told me to use Tri Flow, just a drop on the key or a drop in the mechanism, works great.
I put a drop on the key, work it in and out and turn the lock a few times, then wipe the key off.
One problem with graphite is people tend to use too much, then it can gum up especially if a liquid lube is used afterwards. So if you use it, do it sparingly and don't add anything else.
I use a 3-in-one graphite spray made for locks.
Give it a shot and then work the key to get the tumblers lubed.
Does your lock still have the rubber cover? It helps.
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