Easy fix.
Oil seal pushes in from outside.
Hard part is to get the shaft shinny clean before you start or it will wreck the fine feather lip on the seal
Wrap the shaft in 2 layers of glad wrap pulled very tight to prevent the key shaft from cutting the said same feather edge.
a good coating of vasolene will make it slip in easier then use a piece of pipe or a small hammer & punch to drive the seal fully home.