Hi,
I had the same struggle with my 1985 500 SL where it turned out the hardtop was stuck, and I could not retract the
latch in the rear center. It took me half a day to get it off, here is what eventually worked in my case.
If you can lift/pry the hardtop slightly up in the back, try to gently force a wisegrip or similar tool
under the HT to lock around the pin and turn it counterclockwise enough to go free of the latch/hook on the car.
With a few helping hands lifting in the front and turning the hardtop to the right similtanously might also help if you can't turn the locking pin
sufficiently around. ( about 90degrees approx)
Good thing in my case was, that when I finally got the damn thing off, an original unused as brand new softtop revealed itself, indicating
the hardtop probably had hardly if ever been off the car.
Hans