One has to be able to drop the pan enough to get the rear cap off. The BOP rear seal is pushed through the groove with sealant on the end a few times to fill the rope seal anti-rotation holes. once filled the seal is then wiped clean an rotated through a few more times to clean the groove.
the seal is then slid in and the cap is placed on with the other half of the seal and torqued down. The BOP rear seals are very good.

trouble is some of the seal grooves are not concentric or the mains have been machined so many times the groove has tightened up on the top and bottom. That happened to me and I had to make a tool to remachine the groove.