Just found this bit of info:
Note: Whenever you have a shaft pulled, it is a good idea to check those snap rings, or "circlips" on the inner stubs (no, they are not "C-clips"). There had been a rumor that the inner grooves of the traction-lock carrier could have been machined incorrectly, making the snap rings fit extremely tight (and susceptible to damage when they come out), but I have never been able to confirm that. My $0.02 is that since some rings are made from flat stock - like the ones I had - it causes them to catch on the inner groves, hence the extra force needed to extract them. If you have those, grab another set from Ford, 1L2Z-4B422-BA, which hopefully are a round wire and will allow the axles to come out much more smoothly. If you still have trouble, a 1-5/8" tie rod separator, such as the PowerBuilt 647056 works great. You can rent the AutoZone set with that one in there, or buy one of your own for the tool stash: a couple taps with it between the differential and hub will pop the axle right out!
My axles were an absolute pig to remove, so maybe this is why? I will try and source the part number mentioned and see if they fit.
Struggling a bit. Ebay is going to cost me $40 for a 50c clip that I don't know will fit. No luck on RockAuto.