I own a 72 W108 with a moon roof and can't figure out how to get it to open. The motor works as I can hear it and can see it moving gears or something in the roof above the rear seats under the head liner. When I try to open the roof it makes a noise like it is going to open but is stuck and when I press the button to close it makes a grinding noise. I have accessed the manual opener in the trunk and loosened the outer bolt and cranked it both ways. One way will not budge and the other way makes that grinding sound. I have no clue where to go next. I think it may just be stuck from lack of use and need greased but I can't manually open. Any suggestions??