I've got one of these aftermarket sunroofs on mine, it was leaking and raining like yours, but the previous owner had already siliconed it up. I took the glass out (very quick) using the clip, removed all the silicon, got a sponge and warm water and cleaned all the crap out of the grooves around the seal. Once dry I sprayed some silicon SPRAY, the stuff used for lubricating, on the seal.
I thoroughly cleaned the glass sealing surfaces with window cleaner and replaced the glass.
I haven't had a drop come in all the way through the winter and I can open the sunroof when I want to. As long as the seal isnt perished it should just need a good clean and lubrication with the spray.
Might work if you want to use the sunroof at the moment
