It could be brass /bronze which could contribute to the breakage. It
could be silver braze alloy corroded with age.

Sweat the old one out with a torch. Try not to burn the braze alloy.

The only problem may be with the new insert. Not all carbide wets
well. Put a good amount of flux on the new insert with a cut bit of
wire and heat it. If it flows out well then it is good.

tom