In theory, you can change the seal without completely dismantling the engine, but it will be very, very difficult to slide the new upper seal into place. Coating it in vaseline should help. I'd definately try it before pulling the engine.
You need RTV from the each side of the bearing cap cut-out to the seal and RTV along each bottom corner of the cut-out. Not too much. I find the nails sometimes tend to puch the side-seals down a bit at the final tap or two. So RTV can fill that space up too. Let it cure before installing the
oil pan.
I currently have a leak from the dipstick tube where it joins a nipple on the
oil pan. Left front top of pan. Under the car, all the
oil appears to be coming from the rear seal, but its not. Rushing air blows it back.