Useful advice on sourcing teflon blocks and more details from Sealing heater edges with silicone on replacing the heater, particularly this gem of an idea that I intend to steal use:
I’m going to mount the TCO on the heater using the high temperature silicone so that if the heater peels off the plate again it might prevent damage or fire by staying with the heater.
A live link to the source, Plastics Remnant Outlet, of teflon block that he found:
https://www.ebay.com/itm/2-Teflon-Block-Sheet-PTFE-White-3-75-x9-5-Cnc-Plastic-4636/254184742296