I tend to get some buildup around the top punch of my seating die so I clean it occasionally with some Hoppes. Also, occasionally my sizing die will get some grit in it that I need to wipe out. I only do this when I actually see something, not on any regular basis.
Hoppe's does a good job for the sizing and expanding dies.
For the seater and crimping die, I have used Brakleen with good results. Squirt and scrub. Either that, or a good swabbing with denatured alcohol will clear out all the bullet lube and gunk from these dies.
With either method, oil with a light lubricant (3-in-1 works great) before storage. Also, remember to use the solvents listed with good ventilation (do it outside!!) and wear some good gloves.
The case lube on the lead bullets is the main problem. Some lead bullets have a lot of waxy lube and I have had to clean seating die every 200-300 rounds or the OAL goes short. There was a guy in NJ years ago who formed hard lead bullets on a cold header as if he were maiking steel bolts. They had a very hard lube and I could load several thousand rounds with very like crud build-up. I have not been able to if this outfit for several years.