I'm confused here...a 1977 E39??
On the E34, I remember it's just lifting up the whole panel from the bottom,
then pull off. There are clips on top and bottom, the bottom kinda catches on, that's why the lift.
On the E39, I have not taken it off, but I think I recall seeing my mechanic unscrewing 2 screws on the bottom of the panel, then pull it off.
Someone might be able to confirm that.