George and Charles:
I've also used Tufo sealant in tires without removable valve cores with mixed results. And had the Tufo stuff congeal in the tube in less than a year, so check for freshness before a ride. I've also had some valve cores freeze-up after using Tufo. On one occasion, it blew out of the 1mm patched hole a few weeks later, even though the tire was only pumped to 95 psi. The inner tube rubber may also affect how well this stuff works. The Tufo stuff came out of a butyl tube.
I've recently switched to two other new products, which seem to do a better job: Vittoria "Pit Stop" and Hutchinson "Fast'n'Air." They're expensive at $15 a pop. The Vittoria sealant has a force-fitted valve gasket that can come loose and it's only for presta (the present company). While the Hutchinson product has a secure screw-on adaptor, which can be removed for a shrader valve.
Michael Allison
New York, NY