Much of what you see is cosmetic, not functional. With the exception of the rotating surfaces, most of that varnish can just sit there forever. To clean the rotating surfaces, put some BG flush in the oil and run it through, then change to synthetic. Over time the new oil will dissolve some (but not all) of the varnish.

A better approach is what Dick suggested: head reconditioning by removing it, cleaning it, and replacing oil seals and rubber parts.