In car, the two piece replacement is a little more complex, especially if it is the traditional rope seal. If changing over to the neoprene seal, there is a retention pin which needs to be removed from the main cap, as well as the customary light loosening of main caps to permit some minor clearance to move the seals out and in. It's not a simple process. The upside is the trans can usually remain in place, if loose, where the trans must be slid back enough to get a one-piece seal out and the new one in.
There are plenty of how-to's on the net, with pictures, so set your laptop up out in the garage and go to town. It's just auto mechanics