Since it is an aftermarket sunroof and you have no documentation on how it is constructed, it might need a bit of exploratory surgery.
I would verify the leak's location before disassembly of anything.
Taping the gap between the glass and the frame and then flooding the roof with water should help verify if the frame is leaking between it and the roof.
Taping between gap between the roof and sunroof's frame and then flooding the glass can test the sunroof's weather stripping.
The weather stripping would be my first guess, as it is more likely to deteriorate. With the lack of drains, leaking water needs to go somewhere.
Are the frame's mounting screws tight?
Let us know what you find, there are ways to seal the frame, assuming a leaky frame is to blame.
If the glass weather stripping is leaking, that usually requires finding the correct profile weather stripping.
It can be taped to temporarily prevent a leak.