way back when (pre-google), canoe parts were impossible to find, so we'd often take a "negative" fiberglass mold from the good cap, then use one of those heavy, thick, flat ABS fender flares, cut it roughly to size, and use a heat gun and piece of rounded dowel to soften and force it into the mold- if the plastic was soft enough, and the mold accurate enough, it would even pick up the patterning or pebbling from the original cap, and the softened plastic would leave bumps where any holes had to be drilled, just take your time and be careful with the heat- too much softens the resin in the mold, causing it to deform or melt, and too little can lead to stress in the pvc and cause cracking, slow and easy, and a good long cool-off in the mold (I waited overnight) has the best results...