How to Fix a Crack on a Ladder Bathroom Radiator's Plug with Water Leakage?

Hello and welcome. Today I noticed that the ladder bathroom radiator has a crack on the plug, probably the plug, from which water is leaking drops (pictures attached). Water is leaking in two places, at the bottom of the plug and in the crack at the top. Since I have never repaired this type of fault myself and it seems trivial, I would like to ask how to approach it? I live in a single-family house, the radiator is on the ground floor, there are also radiators on the first floor
Is it necessary to drain water from the central heating system? New blanking plug mounted on tow? Thank you for all your advice,

There should be a valve under this white cap. If it is necessary to unscrew the radiator, close this valve, turn off the thermostat and the radiator can be unscrewed. However, if the valve itself is leaking and requires replacement, draining the system is necessary.

In my opinion, the thread on the radiator is damaged and I need to buy a new radiator, but I noticed that the valve is sealed with Teflon tape, which I would first replace with tow.
Teflon is good but sometimes it starts leaking.

What are you writing? It is pouring from the return valve cap. There is no need to remove the radiator or rewind the Teflon. The nut needs to be replaced. Whether you find one somewhere is another matter. I think if you look hard enough, yes. The most expensive option is to buy the same valve and replace only the cap. It is not screwed onto hemp, it should have a gasket. There is another way. Try removing such a cap from another radiator in your home. Return valves should not leak, so you will definitely have a tight valve in one of your radiators and you can put the damaged cap there and put the functional one on the leaking valve.
You remove this cap without draining the water.