I asked

> <snip>The seal cap, which caps the differential and is between it and
> the CV joint, was out of position. I examined the seal cap and it
> appears to be undamaged. My question is, can I just tap it back firmly
> in place or do I need to get a new one?

Joel Cort suggested that the cap can be glued back in place with some
silicone. I have some oil resistant gasket silicone sealant that I'll use to
put the seal back in place. I just bought a new set of rear half shafts on
eBay which I'll install. Then I can rebuild the old shaft with a new CV and
boots without being hurried.

> Does anyone have any clue why
> the cap should have come loose in the first place?

In a p-mail, Darrell Boehler said: "No particular reason they should pop out
unless your air vent is clogged. If they are undamaged they should be ok.
There may be a vacuum placed on them if the axles are pulled to the outside
quickly." I think this is the answer. For the past month, the CV joint has
been getting progressively worse. When it binds, the shaft actually bounces
in and out. I couldn't figure how this hammering could loosen the cap. But
Darrell is right, the vacuum could pull the cap lose.

Thanks for all of the good advice.
Larry