If you had some kind of cheap dent puller, with a home-made hook on the end, you might of had an easier job getting it out. The seal you have is the same one that I had in my thread. The outside diameter should be the same and tight enough to seal the lube in when installed correctly. Use something of the same diameter to drive it in square. If you want to make it a little easier to slide in, use a very thin coat of RTV on the outside before tapping it in. I also wipe the inside housing surface with gas or brake clean to get it clean.
Before installing your axle, wipe a little gear-lube or grease on the new lip or axle.