The best thing to do is just to invest some extra money in a wet cleaning set. Shooting for years portraits without a problem and suddenly discovering you have a problem when stopping down the aperture and not being able to fix the problem quickly yourself sucks. So just get a cleaning set.
I did that when I had the issues with the 5D, but I couldn't clean it for the life of me. So I sent it to Canon. Unfortunately at the time I was NOT a CPS member, so it cost me about $200.
I'm very sad that I don't have the Mark IV, but in the end I'll feel better knowing that it got some maintenance. Hopefully that's the only issue they'll find.