It is now some 10 years since I changed the sump on my 3.9 Plus 8 so my memory isn't fresh. I don't remember any difficulty, just be careful as you remove the sump as the oil pump suction pipe and strainer fits through a window in a baffle plate in the sump, so take time to make sure the strainer is lined up with the window as you lower the sump. On these later engines the recommendation was to use a gasket sealant rather than a physical gasket. There was a warning not to over tighten the sump bolts to avoid distortion. My sump did stay oil tight for a long time, it still doesn't drip, but there is a sign of oil around the surface of the flange at the rear of the sump. Could be a good time to paint the base of the sump while it is off. Check the drain plug boss to make sure there are no cracks in the weld. The sump plug is a low point and if it takes a knock the weld between the boss and sump can crack (best not ask me how I know this).
