[Carl n Susan]

What year Montana do you have?
Older models used a two piece frame that screwed together and pinched the glass in between. .Newer models use a two piece frome but the window is held in by a rubber grommet (for lack of a better term).

Both are easy to remove and have a glass shop fab up a replacement piece. You can also make a trip to Los Algadones, Mexico (outside Yuma, AZ) and buy a stained glass replacement for relatively little.