Rear main seal leaking

I've replaced the rear main seal and it is still leaking. I've done this 4 times with the same results. It's a 2 piece seal. It does not fit tight in the cap the seal has a gap in it. Is there something else I can do? The truck listed above is a 1500 with a 5.9 ltr v8 mag. Which I didn't have to drop to access the rear main.