kcblair I have had similar experiences with sealant in Tufo tires. My experience was with Tufo Tubular Clinchers but I imagine the construction is similar. The sealant would work until you were out on the road a while and then not. I've had good luck using sealant in Continental Sprinter and Competition and also Vittoria Rally and Corsa.
A plug in a tubular tire would have to find its way into the inner tube. I'm not sure that is likely.
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I don't do: disks, tubeless, e-shifting, or bead head nymphs.