I recently replaced my 1969 AMF Alcort Sunfish lower spar with a donor spar that was the upper spar on a Super Sailfish. I moved all the original hardware, blocks and the straps that hold them over and added fancy thick sticky tape to the gooseneck area to prevent the corrosion that forced this work. Today I added new corks inside the spar. The bow end has the interlocking eye bolts and its easy to see that the endcap can't really be made to be airtight. I took the endcap down to the hardware store and was suprised that they had four drawers of Midwest Fastener cork stoppers. These are the aggregate type, not the natural cork type used in the 60’s but close enough. Size number 18 looked correct when held up to the endcap, slightly bigger than the outside diameter of the spar. They were $2.05 each. I bought a pair. Back home I relieved the inside edge of the spar with emery cloth and also cleaned out old caulk. I used silicone grease to lubricate the cork and the inside of the spar. To avoid damaging the cork. I held the flat end of a ball peen hammer against the cork and tapped the ball end with another hammer. I bought the silicone grease at the same hardware store a month earlier in the plumbing section. That type of grease shouldn't attack the binding glue holding the cork together (time will tell). The outhaul end was fast. PB blaster on the pin holding the endcap. Forced the pin in using a small nail after dulling the point. Took off the encap, saved the pin and did not loose it! Installed the cork in the same way, put the cap on and tapped the pin in. As far as masts go, A few years ago I used the advice on the forum to use a racketball in each end. They do the job.