I mean if it has to leak this is a good place. Still I would like to get it fixed. Where to Start? I assume there is a gasket between the inner and outer plastic?
If it's not cracked, clean the sealant from around it on the roof, then reseal with self leveling sealant, such as Dicor brand. Do not use silicone, as nothing will adhere to it, not even more silicone. While you're up there, check sealant around all vents etc. Also around edge of roof. Hope this helps.
I would check for any cracks in the plastic also for cracks around the mounting screws. If no cracks or visible damage then check the sealant especially around the mounting screws. Any good self leveling lap sealant will suffice. Dicor or an equivalent will work. Here is what is used at the plant.