I think the "correct" thing would be to tear it down, clean as much as you can by hand, then follow the manual on oil change intervals. But who has time to do that for sludge? Seafoam according to their bottle can be put in the oil. But two things, probably not approved in the manual, possibly even forbidden. And you run the risk of it taking this sludge build up off in chunks and clogging oil passages.
I see oil changed more frequently helping, how much would have to be confirmed by some of the guys on here. Personally I don't see it making a noticeable difference from the little experience I have.