Help! Previous owner caulked the window panes into the sash rather than applying glazing compound. I've broken two window panes trying to get this stuff out with a putty knife, and I've broken three blades trying to cut it out with a utility knife. I'm nervous about using the multi-purpose tools with the caulk cutting blades as the caulk is applied direcly to the glass. Any suggestions to help me keep both my sanity and these historic windows intact?