The question is can I remove the glass by removing the four small screws holding the tabs and lift out the glass?

Yes, you can! I found it easy using a power screwdriver. Might need a torx bit. Very helpful to have a helper for lifting and moving the glass unit. I installed a non-leaky used unit when the dealer said the only leak cure was a $895.00 new one.

My 960 is a 965, so the mounting of the frame might be different. It does seem to me that for the sunroof to sag there must be something else going on, though.

The seal around the glass unit that fits into the roof hole is mounted on a frame piece that is glued/sealed to the glass. Look carefully at that frame piece, maybe that's what is sagging.

While you can see the tracks that the guide pin follows as the sunroof opens, slather on some good gooey lithium grease, the spray stuff isn't good enough.

Good Luck,

Bob

:>)