Clean reloading dies with a degreasing spray. Be sure to wear eye protection. Gloves are also a good idea, even though they are not shown in this photograph.
Lubrication is a messy, but necessary evil when resizing cartridge cases. It takes time to apply and then has to be cleaned off before firing the cartridge, but without it you can’t resize rifle brass. Sometimes though, it seems almost as if lubrication’s main job is to cause problems. If you put too much lube on a bottleneck case it ends up with dents in the shoulder. That happens sometimes even if you put on exactly the right amount of lubrication because of the lube that builds up inside the die. In that case, you must clean the inside of the die before using it or the problem will persist. Use a good spray degreaser to blast out the gunk, but make sure you have eye protection and that all your skin is covered, as it will splash back. It’s nasty stuff; you don’t want it on your hands and you really don’t want it in your eyes.
Remember, once you have cleaned the die it is bare metal, which can rust quickly. You must protect it. Most rust-preventative sprays work on the outside, but use case lube on the inside. Remove the depriming stem, spray lube inside the die, then use a patch on a cleaning rod to wipe out the inside so there is just a slight coating left behind.
Just as with plumbing, sometimes the problem is a plugged hole. Most dies will have one or more small relief holes drilled in the sides to allow excess lubrication to squeeze out. If you are getting dents in the shoulder, often these are plugged. Use a straightened paper clip to poke through and make sure they are clear and open.
Don’t worry too much about the dents in the shoulder—unless they are huge they don’t cause any major problems, but they sure are ugly. When you shoot the cartridge the dents will iron out and the case will look fine again. If it bothers you, use that ammo for practice.