I read a number of "answers" on this topic, but none seem to cover my type of drain installation. BTW - Tom (speedball1) had a number of nice explanations.
First of all, it is my 2nd floor shower drain that is leaking, as there is discoloration on the drywall ceiling directly below the drain (in the kitchen). We just moved in to this house which was unoccupied for a year so it is hard to tell if the previous owner had the same problem, used the other upstairs shower, and just repainted the lower ceiling.
Anyway, the I ran a hose down the drain and didn't notice any further wetness on the ceiling below so it seems to be immediate drain area. Also, when showering, there is no standing water in the shower floor (the shower drains well). The stall is a fiberglass type enclosure and is well caulked at all seams.
Attached is a picture of the drain after I took off the strainer cover and scraped off a black "gasket -like" ring which was brittle and easily broke into three pieces when popped with a screwdriver. My question is: Is there an obvious fix for this situation? I looked at the WingTite Replacement Shower Drain, but the instructions on how to remove the existing drain are not really clear. I seem to have a 2" PVC type stub which is cemented in place around the circumference. What do I need to "cut out"? Would I cut all the way to the metal ring?
Also, do I really need a whole new drain, or can I just re-caulk the top area with silicone?
I'm pretty handy with do-it-yourself repairs, but I like to know what I am doing?

Thanks in advance for any expert replies.

We may have a couple of issue here. The space between the 2" PVC and the chrome ring should have been filled with a ringed collar about 1.25" tall. It is usually black and you might have been chipping the top layer off. I would continue to clean out that area with a lot of picking or needle nose pliers. You can fill that area with a good silicone if you can't find a replacement collar at a plumbing supply house. Now for that chrome ring, I can't see under it but it should have been set with a good ring of plumbers putty and we don't know that it was done properly for sure. Clean the crevice between the shower fllor and the ring with a screw driver and maybe a dull knife tip. Apply silicone to this crack and wrip it with a wet finger tip. Jiggy rigged to be sure but I think this will give you several years service. Sad news is that ceiling material probably should be removed if it has been wet several times over the years.