You don't want too much play there. MB purists waste entire afternoons (usually the same ones who waste entire lives trying to get their 1973 diesels to run perfectly) measuring the axial play with a spring-loaded dial indicator, but the Volkswagen method of a just-moving washer is probably even better. Basically, you want no axial play, but you don't want too much preload on the bearings either.

As long as you get the cap on snugly, with no dents around the seating surface or holes in the cap, it will seal fine.