I recently purchased an inexpensive cast aluminum oil pan for my 1991 5.7 gmc engine block with the passenger side dipstick and one-piece rear main seal. The gasket is a one piece blue fel-pro gasket. Last night I did a quick test fit and it looks like it fits pretty well except for the radius for the rear seal area looks like it is a little different. It looks kind of tight top to bottom. The sides where the pan meets the block looks like there may be a slight gap. While brainstorming, my possible solutions are: 1.. weld new aluminum to thicken the side and reshape the hole. 2. torque to spec with added silicone to the sides 3. add filler solid gasket material and silicone to the sides. It was from ebay and for the cost, I will not be returning it. It looks really good except for the one fitment issue. If you have experienced this same situation, or have a better idea, I have open ears!