Sandwich your old seal between the driving tool (such as PVC plumbing fitting) and the new seal. You will feel it when the old seal bottoms out in the chamfer. For the crank seal, it's not even an issue because the seal sits at the bottom of the bore.

 

Already finished it several days ago and just dropped in the engine(haven't run it yet). I did measure the inner, mid and outer edges all around the seal for uniformity before and after. I have not found that the plumbing fitting is at all accurate. In fact, very inaccurate. When you slowly tap against it with a block of wood & a mallet, it does drive it in and it certainly looks to the eye like it is driven in uniformly, but after measuring, I found it to be offset from one side to the other by .002". It took a lot of careful, precise tapping, and measuring to get it right, and also not to overshoot the depth, while getting it uniform.

 

I will re post if I have problems. It may take a while as from reading past posts that they can leak at about 7k-10k miles later which sounds about right.

When you slowly tap against it with a block of wood & a mallet, it does drive it in and it certainly looks to the eye like it is driven in uniformly, but after measuring, I found it to be offset from one side to the other by .002".

Using an old seal helps to drive the new one in squarely, although such high accuracy may not be guaranteed.