To remove the old seal I drilled a screw into it and pulled it out with vice grips and a slide hammer.
To install a new one I fumbled around, got a clamp, a large socket and a mallet to pound the seal into place. If you're just concerned about the seal, that's great. I had to do a complete overhaul last week and it's so simple that a 12 year old downsgirl could do this without trouble. If you ever have to do a complete overhaul, be glad it's a simple transmission and not some huge overcomplicated mess with a fragile wiring harness at every corner of the valve body.
Good luck with the seal. I'm going to be spending today trying to reinstall my transmission. I have trouble clearing the exhaust lines.