My Onguard lock, that has served me well for over a decade (I have 2 of these, the other one has been in use for almost 15 years), had some of the pins stuck, preventing the key from going inside all the way. Oil didn't help so I disassembled the lock, cleaned the parts and found two pins that had some slight wear/sharp bits from use that lodged them in place. I filed the sharp edges off from the pins, reassembled the lock and now it seems to work ok. While at it I learned how to serialize these locks and read the serial number of the lock from the key.

The whole affair took about 2 hours because I missed one of the worn pins and repeated the procedure several times before finding the last culprit. It's a miracle none of the almost invisible springs got lost!