I have seen this too and thought I would be giving it a try. Thanks!No, your correct it does not have to be the exact diameter as long as it fits.
Also, I was just looking at some other videos on removing the ceramic seal and I ran across this one. I can tell you for sure that you will be cursing the seal when you are in the process of removing it. This guy has come up with a procedure that I have never seen before, but it looks like it really works and makes it much easier. If I every have to change another seal, I will probably give this a try. Can am water pump seal tips ( will work on other bikes too ) - YouTube