I recently noticed that the 4" brass cleanout plug is leaking. It is barely threaded in 1/8" because of galled & crossed threads. Is there someway to fix this. A 4" pipe tap is pretty expensive

Brass is softer than cast iron so it should be the plug that is damaged not the pipe hub. Replace, you can even use a PVC plug.

Agreed, I'd go with PVC and even coat the threads with compound or teflon. Cast thraeds can be rough and pitted.

Agree with Experts above... Also, take skinny flat screwdriver and clean rust from inside of threads before you install new plug.

I recently noticed that the 4" brass cleanout plug is leaking. It is barely threaded in 1/8" because of galled & crossed threads. Is there someway to fix this. A 4" pipe tap is pretty expensive
Take a wire brush and clean up the threads, Wrap a few turns of Teflon Tape around the replacement cover and start the threads correctly. Tighten until you feel the cover's seated firmly. Good luck, Tom