Moderate use of a quality CLP such as Ballistol can be used to protect the metal parts of your handgun from the hazards posed by corrosion, friction and also fouling.
You just started collecting Social Security and are now fully retired from the day-to-day rat race of making a living. This is the time in life you had been looking forward to, which equates to unlimited range days with your favorite pistols.
When dealing with two similar calibers like the 9x21 mm and the 9 mm one must be particularly cognizant that the ammo used matches the caliber stamped on the barrel to lessen the possibility of potential damage to yourself and/or your firearm.