With your car being a 1997, I'd most likely say it's a Seperator plate... Just for future reference, if anyone ever has their engine out for any reason, and has a plastic seperator plate, Replace it while the engine / tranny's out! You'll save alot of time and money later on! You can order it from the dealer (Part Number 11831AA150) or you can PM me, and I'll sell you one for 13.00 plus shipping.
If you're going to be doing the work yourself, and you don't have access to a hoist, I'd recommend pulling the engine. You have to pull one or the other. You can look at the rear main while you have it out, but I doubt it's leaking... I think I've only seen one rear main seal on an EJ series engine leak and that was because the plastic plug that covers the access hole for the torque converter bolts got stuck inbetween the flywheel and the block, and poked a hole in the seal.
The seperator plate is a very common issue from 1993-1999. 1990-1992 they used the Aluminum plates and we never had a problem with them. in 1993 they went to the plastic ones, and we had all sorts of problems with them getting hot and warping, and then they'd start to leak. They finally fixed the problem (aka went back to the aluminum plate) when they went to the phase 2 engine in all of the cars in 2000.