I do not use sea foam in the engine oil .. good if you have a fuel injection issue put it in the gas...

I use marvel mystery oil in my old 25 plus year old engines because I do not use synthetic in those motors...
I only put in 1 oz per quart of oil cap.. of MMO.. one engine has 5 qts so 5OZ of MMO.. this will slowly breakdown the sludge and clean up the pan and oil filter screen.
you said a small amount of sludge on the heads.. so looks like you do the oil changes properly. on all my engines I do the oil changes and run the engine for several miles so it is hot.. then I give it 45min for all the oil to drain out.. I would cut open the oil filter so that the filter media looks good..