I just replaced the mechanical seal on my CX , with the engine out, and I thought I would pass this on as it might help someone else. I used the Yamaha seal.
I used the Dremel tool shown to enlarge the aperture. It seemed to be creating a slight bevel in the opening and I didn't want to go too far. On my first attempt to drive the seal into the hot cover, with a socket, I found that because the socket had an opening that was tapered on the inside that all the force was applied to the outside edge of the seal. This started to bend the metal of the seal rather than driving it in.
Looking through scrap I found a piece of 1 1/4” pipe. When cut square with a saw it was also a bit large with a 1 1/18” I.D. Opening, but when cut with a pipe cutter the pipe was knurled inward and the diameter was reduced to the point that it was slightly too small. I touched up the end with a grinder to make a flat landing and opened up the inside slightly with the Dremel tool and it fit perfectly. I also opened the aperture on the case a slight bit more and the next attempt was easy and apparently successful.
Home Depot will cut the pipe and make a cheap and effective driver for you.