Grandson drives an older Chevy (2000 or so).
Transfer case developed a leak from some sort of factory flaw. He scrounged up a used case and installed it while he was at the University. It worked OK but he skimped on tools and tried to use large sockets. Seal didn't hold so when classes got out for the year, he asked if he could use the lift in my shop to fix the seal. Seal driver is $120 or so. Gramps figured he could crank one out for less and that proved to be true because the poor guy works pretty cheap, and especially so for certain people.
The seal is a bit complex and includes a Speedy-sleeve that is incorporated into the seal assembly. After making a driver and using it to install the seal, I can see why a half way approach would fail.
Here are pics of the driver and one with the seal sitting on the driver face. It's good to have a lathe and I guess, a hoist. Grandson agrees with the old guy.

(driver (full).jpg)

(seal driver (full).jpg)

driver (full).jpg (114KB - 46 downloads)

seal driver (full).jpg (105KB - 46 downloads)