Arrived in a day with another (brass) lock. A fiddle to fit because the door handle and plates had to be removed. This particular lock was very difficult to use in the first insance, being extremely difficult to turn the key, sometimes requiring two hands! Something seemed to be fouling the mechanism. (There were no problems with the other lock.) I telephoned Yale and they advised lubricating, suggesting that the lock had been in long-term storage. Without much expectation because there seemed to be a solid obstruction, I applied WD40 via the door edge hook hole and GT85 around the lock barrel at both ends and into the slot. After operating the lock many times, there was some improvement; more so after leaving the lock for some hours. After several days and some usage, there was some more improvement. I intend to insert more lubricant soon and re-assess the lock.