Commercial flat roof drain bowl

I am working on a 20 year old flat roof in FL.  I have encountered a drain that has a 2-piece bowl.  There is a gap at the bottom of the inner wall and when I am testing them, about 30% of them leak.  This is a new roof with 3 plys of mod bit roofing over a vented base sheet.  Around the drains, there is an additional lead sheet and target patch under the cap sheet.  The membrane itself is not leaking and it is not leaking between the bowl and the membrane.  When tested, the drains leak down to about an inch below the top of the bowl and the water level stabilizes at that point.  The roof is over tapered lightweight concrete.  Has anyone else encountered this type of roof drain and do you know what type of drain it is?

Look at the icon in the formatting bar right above this line.  You should be able to upload a picture by drag and dropping.

If you upload a picture, then we will able to more accurate answer..

Have you tried tightening the drain nuts? I have seen those drains and they normally have a rubber gasket between the top and bottom. However , sounds as if the water may be migrating through the drain stud. Like coery1 said, pictures would be helpful.

DO you have pictures?