Radiator leaks sound minor but they can actually cause a lot of damage to a home. If your wood flooring becomes wet continuously it will rot over time. A small radiator leak can also cause unforeseen damages to the ceiling below, which later can result in a mold issue inside the space between floor and ceiling.
In this video: https://www.thisoldhouse.com/how-to/how-to-repair-whistling-and-leaky-steam-radiator , This Old House plumbing and heating expert Richard Trethewey silences a leaky, squeaky steam radiator.
1. Turn down thermostat to shut off steam-heat system.
2. Wrap Teflon tape around the threads on new air vent.
3. Twist off old air vent by hand; cover vent with cloth to protect hand.
4. Thread new air vent into radiator. Hand tighten vent to vertical position.
5. Unscrew handle from top of the radiator valve.
6. Use an adjustable wrench to loosen and remove the packing nut that holds the stem to the valve.
7. Wrap graphite packing around threaded portion of the valve stem.
8. Thread the packing nut back onto the valve and tighten with a wrench. 9. Replace the valve handle.
10. Turn up thermostat to start the steam-heat system. Check for leaks or high-pitched whistling.