I have a failed IGU (insulated glass unit - dual pane) in an older aluminum window. I have another good IGU (from another spare frame) that I wish to substitute for the failed unit.
When I try to separate the IGU from the frame it is stuck to it by a black sealant. I tried using a breakoff knife and putty knife but they don't work.
Without breaking the IGU, what is the best way to release the glass unit from the aluminum frame?