Just recording my experience for those that will follow.
My sunroof on the '38 SS 2.5 saloon was not raising up in the left rear corner when I turned the locking handle.
So to remove it, of course I first read the manual. The '38 Instruction Book did not cover the sunroof. So I looked in the '46-'48 Service Manual.
Page 95 Operation 100 says there is a small hole for a pointed tool. Nope, not on mine, no place for a “pointed tool”.
There is one visible screw in each front corner. I removed them, but nothing seemed to improve. I removed the narrow cloth covered strip along each side of the sunroof panel. Two screws on one side, four on the other, must have been two different factory installers. Not the polished wood strips, these do not need to be removed at all. This exposed two more screws on each side holding the catch mechanisms. Ok now it lifts up a bit, but it’s not coming up much.
The manual now says a sharp tap with the pointed tool will release the spring toggle. Nope, no spring or toggle on mine.
I discovered that with all 6 of those screws out, if you turn the handle to lock it, the front catches move outwards, just enough so you can get one side off, then the other side. They are 3/4" wide slide hooks on pivot pins, so you may need to lubricate them before they will pivot enough to unhook from the fixed slides.
Then the front will lift up and you can slide the roof out.
There is a metal tray between the sunroof in the open position and the head liner, which collects dirt from rain water, so clean it out in there.
Here is the offending left rear lifting mechanism.
The loop had come unhooked from its clip. Hooked it back on, squeezed it with pliers so it won’t come off again, and it’s back to normal service.
BTW it is very tricky to get those 6 screws back in place in the threaded plates in the catch mechanisms. Use a small pointed tool to line them up. 
