don't interfere with a heating system unless you're competent; i did, and i wasn't; guess what happened? big plumber's bill, and i'm actually a qualified tradesman in a related craft! ever heard the old saying:- if its working, why fix it? ; i know lots about plumbing now, but it took me ages to learn; i learned most from my mistakes! my advice, leave well alone! just sand off as much of the rust as you can before priming, then paint with an eye-catching colour thereby making a feature of that tired old rad; don't paint over the connections if at all possible; if you're really determined to replace the rad, then send me a pm and i'll explain what to do;