akirby, Thanks very much for the reply, and for the info that it is pretty rare to have a main seal leak, and the info on the 2.7 L oil pans. (we have the 3.7 liter) We have had regular oil changes. Got the vehicle back a couple days ago, (Lincoln Dealership) and they said it was the rear main seal- and so far, no more leaks. I know I mentioned the recent attempted repair history in my original post ( 12-28) but will mention again, that this was the second Lincoln dealer I took the car to for an oil leak repair. I gave the first Lincoln dealer (where we purchased the car) two different "tries" on fixing it- they replaced the oil pan gasket each of the 2 times it was in, and also replaced the front seal once during the 2 times it was in. To me it appears they missed the leak at the main seal- and I do understand that often it is not easy to find the source of the leak. I think the only other possibility is that there was a leak at both the oil pan and front seal during the times it was in at the first location, and somehow between the time i stopped taking it to the first dealer and the time I took it to the second dealer, (about 2 weeks) a leak started at the rear main seal. I'm not a mechanic, and despite the fact that I know nothing about oil leaks, this "only other possibility" seems a little ridiculous to me.
I think they just missed the leak at the first place. Both times. Thanks again.