During my annual last August, I noted that all the bottom plugs on my Hi-Compression O-290-D2 had lots of lead balls down in the wells. So for the last ten months I've been adding TCP at each fillup. I pulled the bottom plugs today and they had just as much lead fouling as before, only not balls so much, but rather chunks. I dug them out with some .040" safety wire, then blasted with black diamond. So for me, TCP didn't do anything that I can see. I learned that I need to clean my plugs at least every six months, though.