Nathan,

I've noticed that methylene chloride paint stripper tends to dissolve old putty,
though not really soften it. I've used a putty chaser to good effect when
salvaging old glass from bad sashes. It won't get all of the putty but the
stripper will finish it up.

-Ken, who's just as glad he no longer has to worry about salvaging old glass and
repairing old sashes