I have a very slow dripping leak along the boiler return line
(threaded black pipe), a few joints away from the actual boiler. I
would rather not repair now as it's too cold to lose heat for a day:
drain the system (and finally install shut offs on either side of the
boiler!), cut the pipe, install a new union, refill, purge air, etc.
It looks like the pipe dope on this specific threaded connection may
have been insufficient.

Is there anything that I can apply to the outside of the joint (epoxy,
etc?) that would stop the dripping until I can deal with this next
Spring/Summer?

Thanks.
-Theodore