Daisy,
If it is the stuff I think it is you can get it from Airstream direct.
When I first got my 1978 Ambassador I had a few leaks in seams that I could
not locate. The techs in Jackson Center sold me a oil can type thing full
of this grey sealant. They told me to take a utility knife and remove as
much of the old sealant around the seams as I could. I then laid a bead of
this stuff along the seam and it sort of sucked up into the seam. Dry as a
bone now. I did every seam...was an all day job. I used it around windows
and everything else I could find that could leak. It cost about $20 or so.
They said when I run out to bring the can back and they would fill it up
again. After doing the trailer I have about 1/4 of the can left.
Thomas