cleaning steam radiator

steve g_2

I have a single pipe steam radiator, properly pitched, new vari-valve air vent. However, it heats unevenly, even when riser is hot and radiator valve is fully open; the vent pants and I will get some water dripping near the connection when steam is going full tilt. I may have "egged" the brass fitting at the valve/riser connection, putting it out of round. That would explain the dripping. I suspect it may have sludge, and that it is trapping air even with a new valve. I would like to know about cleaning it if anyone could help me. It is a National Art Radiator, approximately 20" high by 30" across, 6" deep, c1940.