I went ahead and ordered a new MC and new wheel cylinders. Brakes are the most important part of a vehicle in my opinion. I checked the MC once again and down in the throat of the fill tube is absolutely packed almost solid with black gunk, almost certainly decomposed rubber. Who knows what someone put in the system in the past. I will flush the lines thoroughly. I plan to use DOT 5 as I purchased a large bulk supply several years ago when it was cheap.