Are you sure that it is the rear main seal? Try loosening the bearing caps one at a time to see if the crank will turn. If the binding is happening at one of the two mid caps, check to see if they are installed in the correct direction. The front mid cap has an F in the casting indicating the side that has to go toward the front and the rear mid cap has an R in the casting indicating the side that has to go toward the rear. The F and the R aren't always obvious, but they are there if you look closely. The caps will fit either way but have to be installed with the correct orientation.
Reversing one or both of the mid caps can create the same symptom even if you check everything with Plastigauge first. Everything looks great, so you put in the rear main seal and torque down the mains, then you scratch your head wondering why the crank won't turn and blame the rope seal.
How do I know about this? Even with knowing better and careful labeling, I somehow reversed the rear mid cap on a 235 rebuild about a year and a half ago. The good news is that the binding crank alerted me to the issue, so it was easily corrected without any problems.
Matt
