A picture is worth a thousand words:
Here is my thousand words:

Here is my thousand words:
- I have lived in a multi unit rental building for a number of years
- I was painting one of the rooms slowly over the course of the past couple months.
- I painted the radiator a month or so ago (for anyone worried about the plain latex paint and ****ty job.. I was going over several existing coats done by past tenants; I didn't ruin anything that was nice)
- Then I covered it up while I did other stuff in the room
- Today was *finally* the day to finish up and as I untaped the plastic sheet from the wood floor I saw this water damage under the radiator. The water couldn't evaporate due to the plastic sheet.
- Then I took the sheet off the rad and the source is pretty obvious!
- I've used a straw to kind of direct the water into a bucket but it's really coming out fast. There's about 400mL in a little over an hour.
- It was not like this before as I would have noticed it at some point especially while cleaning, priming, painting.
- Somehow my painting it has caused this??
- How could painting have caused this leak?
- This thing is in a corner and there is a wall a few inches away so I don't think I could have bumped it with a tool or anything.
- Could I have broken it while washing? If I did that, would it be reasonable to say it was already busted?
- I find all the rusty water coming out to be pretty suspect. But is it normal?
- I am afraid my landlord will blame me for this as he hates spending money and gets real mad anytime anything is required. So I would like to know going in what's has transpired
- By the way I am not looking for legal or communication advice or to be told I should move.
- What is *supposed* to be here? I looked at the other rads in the unit and they all have different components. Is there meant to be a cap on this pipe or is something snapped off or what? I can't find any pictures online that look like the right configuration.
- What's a likely (short/long term) solution to this?
- If I could manage to turn that little knob can I close it? I definitely don't want the whole thing to break off by accident. Like if it's all rusty. I do not understand the anatomy of radiators.
- The knob that's supposed to be at the bottom to let you turn off the water coming in is gone. Looks like it was sawn off flush with the large hex nut.