On Mon, 27 May 2013 12:49:48 -0700, croy
wrote:

But before you goop things up, keep in mind that the elegant
o-ring is dependent on clean, smooth, scratch-free surfaces.
And the o-ring has to be pristine. Never use metal tools to
dig an o-ring out its home. A strong hand lens and strong
lighting are essential for inspecting o-rings and
o-ring-groove sealing surfaces. The slightest scratch
across the surface, or the slightest nick in the o-ring
itself can be un-fixable with lube. An eyelash can cause a
serious leak!

O-rings become deformed. In pools pumps, they may flatten on one side,
so not to seal. Then leak.