I'm curious as to which brand of primers you are using. I have never had a problem with gunk in the primer tubes on either of my 550B's. For the past year and a half I have been using wolf primers almost exclusively. Prior to that it was Winchester, CCI and Remington. Out of the 50K primers I have used in the past year, 45K of them were wolf.. Blitzfike
Federal ... some CCI. I don't know what the deal is. Our reloading is in the house in a spare bedroom so it's not like it's out in the dust or anything. God knows how many bullets we have loaded since we got it but not as many as you have I don't think.
Not so much "gunk" like wet and sticky. More like the residue you find in your gun when you shoot a lot.
Is working like new now ...