I am a homeowner looking for some DIY advice on a leaky stall shower drain. I have owned this house for close to 20 years. I am relatively handy but plumbing is not my forte. The drain in the upstairs fiberglass shower recently started leaking. Tearing down the ceiling to get out the shower from below would be a bit of a challenge. I am hoping that this might be solved from the top. This is what I have done so far: I took off the drain cover and cleaned out a lot of caulk behind it (well it sure seemed like a lot). The 2-inch PVE pipe is level with the floor of the shower. I took some sandpaper and cleaned the area around the drain and found that there is is a brass drain and between the brass and the 2 inch PVC pipe is filled with grey hard material that I cant identify. See attached picture. I have, of course, been searching the internet and this does not look like the other installations that I am seeing. My search, however, found this forum. Can anyone help with the next step? Should I grind out the grey material and try to remove the brass fitting? I would appreciate any help and thanks in advance!