Put the bike on its side. Pull the nut off. Clean it. Put 1211 on the stud and nut. Put nut back on. Let it set up.
Or you can use a copper washer and acorn nut.
RMATV has them..
Front - https://www.rockymountainatvmc.com/parts/all-balls-front-brake-master-cylinder-rebuild-kit-p?v=1685
Rear - https://www.rockymountainatvmc.com/parts/all-balls-rear-brake-caliper-rebuild-kit-p?v=1685