This may give you clues how to remove the panel there are a combination of screws & plastic push fasteners. 2 large screws would be found near the inside door pull being the main anchors. You may find better info in a older Cadillac section of this forum.
There may be warn or loose window linkage hardware parts inside the door that someone should now what commonly wears.
http://www.compnine.com/index.php?u=1&year=1976&artnbr=K14-12&artsfx=NULL&supplgroup=NULL&catcode=61A&modelcode=E&makecode=K&modelseries=NULL&uid=1&modelid=6474&capuid=1&majorgroup=14&grouptype=B
There may be warn or loose window linkage hardware parts inside the door that someone should now what commonly wears.
http://www.compnine.com/index.php?u=1&year=1976&artnbr=K14-12&artsfx=NULL&supplgroup=NULL&catcode=61A&modelcode=E&makecode=K&modelseries=NULL&uid=1&modelid=6474&capuid=1&majorgroup=14&grouptype=B
