People have said use a socket, the official tool, the old seal, and other stuff.

When I did one of my fronts I just used the new seal and the flange. Using the flange to press it on.
Is there something inherently wrong with this method?

 

Just did that job a few months ago. I used the old seal and a rubber hammer. You do need to press it in past the bevel there as I recall.

Not sure what you mean by using the flange. But you won't get a good look at how deep the seal is that way. Besides, with so many other options, I don't know why you'd use a prescision machined/expensive part as a punch.

 

Rather than using it as a punch I used it more as a press. Put the seal on the flange and bolt the flange on. The flange pretty much has to go on straight and the seal ends up set a depth where it's just perfectly flush with the flange.

 

I really don't think you want to do that. You want all the pushing pressure to be on the outside part of the seal where the structure is. With your method you put all the pressure on the lips, which then have the drag the outside of the seal with them. Once it's in, its the lips that matter, and I'm nervous what you're doing to those lips.

As said before, you also don't know how deep the seal is pressed into the seal race.