Heatsink heatpipes came free from thermal pad

Our customer's iMac EMC 2134 is working great, until the 256MB ATI Radeon 2200 graphics chip gets upward of 110C and shuts the computer down. The 730-0481 heatsink simply isn't pulling the heat away. We cleaned it up and applied new Arctic Silver 5 heat transfer compound to no avail. Closer investigation shows that at least one of the two heatpipes has come away from the copper pad that lays against the graphics chip.

Does anyone have a proven way of securing that again so it works properly? This heatsink is pretty impossible to find at this point. Maybe there is an epoxy that would properly join them again and help to transfer the heat? It was probably a very common failure.

Thanks for any suggestions!