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which I take to mean that it hasn't been designed for the newer type of sealant that used for road tyres
Nah the race sealant is designed to plug larger holes but the stuff dries quicker / gums up easier. My understanding of it is that it's the normal sealant + larger more particles, so it coagulates quicker, both sealing a hole, and inside your tire when its sitting around doing nothing.
It probably will still work with a syringe but not a valve core, you'd need to remove it and push it through the stem (you should be doing this anyway)
That Stans thing leaked over the valve and the sealant had all drained into the valve before I needed to squeeze it anyway.