Alan,

If you have the piece that has broken off, just put a dab of Elmer's on it and stick it back on. I don't see anything wrong in repairing a piece as long as the owner doesn't at some point misrepresent it while trying to sell it (which I'm certain would not happen in your case).

If you do not have the missing chimney, maybe you can buy a SEBI that is intact, then carefully remove the chimney and glue it in place atop your hands-on exhibit piece.

------------------
-Art