The efm 520 comes from the factory with a 5 lb tub of
" s o s boiler putti"
stock number bp-5
from s.o.s. products company, inc.
east greenville pa 18041
The tub says on it:
"A ready to use plastic putty for sealing joints of heaters, stoves, and sectional boilers against gas and air leaks when flexibility and not high temperature is the factor. If thinner consistency is desired, add a small amount of any type of oil and knead in thoroughly."
The web site seems broken but is here:http://www.sos-prod.com
They say not sold in home centers..
I imagine efm would sell you some, they seem very helpful.