You need at least a vernier caliper to do this, access to a lathe, even better..
Insert a threaded piece into end of shaft, it threads in.
And make a cup to fit outside of seal, with a hole in the middle of the flat part that fits over the rod ..think spray bomb lid with hole in the end but metal.
Now place it over the threaded part, and touching the seal, then use a washer and nut on the threads, to pull cup and the seal towards the engine case.
Failing making a cup you could use PVC, cut to length accurately, and a big washer.
I think hole in shaft might be for 14mm thread. Maybe just maybe 1.0 pitch.