NEVER use any kind of dope on brake fittings. They are designed to seal without any help. If there's a leak, you have a damaged fitting that must be replaced.
If you mean on a pipe thread, yes it is. The lines themselves seal with a double flair on the tube, not at the threads. Use a little antiseize on the brake line nut threads and slide the nut back and put a thin coating on the tubing so it doesn't seize to the nut. One caveat, if you use teflon tape, leave one thread showing on the fitting where it starts to thread in. Many people have tape hanging over the end and that piece is cut off when the fitting is screwed in. The loose piece of tape can get into places where it can cause problems. Many gas valves are labeled to not use teflon tape for that specific reason.
If the compression or flared fitting is leaking,repair or replace it. Never try to patch up brake lines or fittings. The answer you need is NO.
The thread has nothing to do with sealing the joint. Teflon will not help , isn't recommend, and can cause you lots of trouble if you get some loose little shnitzles in the system. Short answer No
If it's pipe thread, yes. Inverted flare, no. Sometimes I take a 3 way inverted flare "T" fitting and drill/tap one port for 1/8" pipe for a brake light switch. That switch is pipe thread and teflon tape is a must.
i don't recommend the antiseize on any brake system part, too risky to contaminate the system with a petroleum based product.
Try loosening and retightening several times. If that does'nt work take a look at the seating surface, there may be a groove worn in the part. If so replace it.
if you had the need to lubricte the threads, then yes use some on the treads. BUT if you think you would seal a leak.....
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