Just a few random thoughts.
  On the first post I was reminded of the old "wet" clutches that were in 
some Harleys.  I was glad to see them go out of contention, because they 
tended to stick if the machine was parked long, like over the winter.
  Then I thought about relieving the crack's end by drilling a little 
hole so the two walls don't still converge to a high pressure point.  
This can arrest continued crack migration.  If you feel compelled to fill 
the hole, just use high temp RV silicone, available at FLAPS everywhere.
  Then I thought about gas shield welding in place.  An artist and some 
heat insulation blankets secured well might allow an in-place repair.  
You've got some trade-offs to consider.
  Then I realized I'd forgotten that you needed to access the bad seal 
for R&R (remove and replace) anyway.  Just a little thought about this 
R&R on shaft seals.  Consider this.  Take a very sharp fine pointed punch 
and put a little hole through the backside metal ring.  Don't drill, as 
this leaves abrasive particulates.  Then, insert a screw head on your 
body tool slide hammer, and screw it into your newly punched hole.  Next, 
use the slide hammer and out comes that old seal just as slick as can be.
  Sorry for adding to the traffic on syncros as they're outside my 
experience, but these issues aren't.
  John