Sunroof is tuff stuff...
I prefer crank one, because You can always close it...
But to change rusted one will be really challenging.
If it's opened You will need to derust it first, because it is possible to replace it part by part and few screws needs to be achieved in opened or closed position...
Good Luck
Ask freely I've got my sunroof in parts now - the car is beeing painted ;-)