When you use a lubricant in the barrel after cleaning, then stand the gun up in the gun safe, butt down, the oil will run into the trigger group and often will run into the firing pin hole. I have experienced light firing pin strikes on primers due to dried lubricants that have run into the bolt body, found on used guns I purchased.
Exhaustive tests have been done on lubricants and their ability to inhibit rust on small steel plates. Hornady one-shot lubricant won, and Frog Lube came in second. I had been using Eezox for years with no issues, but the tests proved that my favorite was far from being the most effective. WD40 was among the worst.
Moisture can get under carbon in the bore and pit the barrel badly, it is ugly when you see it.
You can upgrade your Kroil to a product called Free All, it is amazing to say the least. Free All is a super penetrating oil that has an ingredient that specifically targets carbon. Free All is available in a spray can and liquid with a trigger sprayer.