Tackled this today with what I can only call partial success. Inspection of the rivets above deck revealed one at the middle halyard exit, one at the steaming light and one a few feet from the top. Not a surprise that it would pull loose. Started by removing the halyard exit plates to reveal large"ish" slots on the port and starboard sides. These were easily removed by drilling out the 3/16" rivets. With these removed it one can see what was going on. The conduit at this point of the mast was resting on the starboard side. Drilled two new holes, one over the other, a foot apart, a foot below the lowest OEM rivet, on the port-side, front, inline with the old rivets. Used a long screwdriver in the port-side halyard hole to nudge the conduit to its home position, then used another long screwdriver on the starboard side to press the conduit against the mast. Then CAREFULLY drilled through the conduit. Riveted the conduit to the mast using the screwdriver on the starboard side to provide the necessary pressure. 3/16"x 1/4" rivets were long enough. Reinstalled the halyard plates and went to check on my work. Using a halyard I was able to seriously rock the boat. The difference was remarkable, but on the really big swings- noise could be heard from the upper part of the mast. Climbed back up, this time to the spreaders. There is no access there, but there is a pad-eye fitting for a spinnaker pole halyard. Removed the fitting and used a flashlight to try to get some view. The only thing visible was the jib halyard. Using a stiff wire, found the conduit on the port side in a forest of halyards. Tried to pull it snug, but it really resisted. I didn't feel comfortable riveting it since it seemed possible to foul a halyard. I assume the next higher rivet is also loose and that's how it found its new position. The mast is much quieter and we can finish the season this way, but it will require dropping the mast to properly repair- next winter. Good time to paint the mast, change the sheaves, replace the wiring and the VHF antenna, anchor light, steaming light .....