>John,
>This is a common problem.  There is a hairline crack in your expansion
>tank.  I had one in mine and I could not see it (at 84,000).  Replacing
>the tank solved the problem.  At the same time I replaced the o-ring and
>the cap to the expansion tank.  I purchased the tank from the dealer for
>less then $60.00 and it included the cap.
>
I don't mean to be tacky or out-do any of the vendors on the lists, but I
have a like new expansion tank from my 85.  The PO changed it to
optimistically fix his leaks caused by hopelessly shrunken and brittle head
gaskets.  Anyway, the tank still has the original dealer sticker on it, and
looks brand new (no discoloration).  Has probably been pressurized about two
or three times.  I would like 30 plus shipping for it.  Thanks, PSD.