Is it still leaking or has it oxidized enough to stop the leak? If so, paint over it and forget about it. Waiting for oxidation is what the manufacturer suggested. I don't like it, because there is no ETA. Meanwhile, our new wooden floor is about to start rotting under it. If it's a pipe threaded plug that's leaking, redo it. The manufacturer is giving us the plugs, but the plumber wants several thousands of dollars for that job. Supposedly, the old ones need to be "drilled" out... Perhaps, we can get someone else to do it for (much) less, but it is still incredibly frustrating.

They both operate on the same principle--conduct the heat of the water through the cast iron into the air. You're trading aesthetics off. One issue is that you need a fairly long run of baseboard to give the equivalent heating "power" (i.e., amount of heat given off by a unit) to equal one of those decent sized old radiators. A heating guy can do the calcs, but when we did a renovation we mostly reused the old radiators in part because we needed a lot of wall if we wanted to switch to baseboard.

We too live in a historic home, one which is heated with hot water and has all of it’s original radiators. Ironically, I was just reading an article about this very same topic, as all of out radiators are painted a glossy off-white and I’ve rec begin to notice some of the paint chipping in places. To give you the short version of the article, the author basically concluded that radiators painted with non-metallic paint produced a higher heat level than radiators painted (or even left bare) with a metallic paint. (they measured it and the difference was nearly 100°) The reason for this is b/c metallic bounces off light particles while flat colors like white & black do not. The very last thing I would ever do would be to cover up these iconic mini pieces of art with radiator boxes, but that is a personal choice.

For a kitchen remodel I recommend you look into a toe kick heater. You can connect to the current plumbing line. This Slant Fin toe kick heater is an example. You will need to run an electric line to power it. The reviews and cost are both good.