Clean both surfaces with scotchbrite pad and rubbing alcohol, let dry, use new tube of a decent brand cyano-acrylate glue such as Loctite or Crazy Glue.
If for some reason that does not work there is a 2-part epoxy made for attaching heat sinks to electronic chips that should work - in fact, any 2 part epoxy should do.
If for some reason that does not work there is a 2-part epoxy made for attaching heat sinks to electronic chips that should work - in fact, any 2 part epoxy should do.