[Walt Fricke]

Right - don't believe everything you have been told.

Guys replace the thermostat seal and the idiot light sender "just in case" because they are a common source of leaks. If they aren't leaking now, they might in the future. And the crank seals on the "while I am there" theory, and because the seal lips could wear as they bear on a moving shaft.

But not these bolt O rings absent finding one leaking. Even then, you'd just deal with the leaker.

Of course, if you split the case you have to replace all of them, as they get mangled on installation, and hence are not reuseable.