Having produced a slot attachment to fit onto the end of my slide hammer, I'm trying to drill a pilot hole into the seal to take a self tapping screw. This will enable me to connect the attachment to pull it out. However, I've found that immediately after starting to drill, I'm drilling into metal. I was expecting the seal to be rubber - the surface of the seal appears to be rubber. Does anyone know if this seal is in fact metal. My worry is that I'm drilling into something underneath the seal. Thanks for any help.

thats correct it has a metal ring cast into the rubber to keep its shape
cheers Tony