: I would highly recommend stretching it before you decide to cut it. Stretch
: over a large bottle, (bigger than your neck) and that will loosten it up
: quite a bit. Most people who cut them (as one poster mentioned) really
: shortens the life of the seal.

My experience has be exactly the opposite. Stretching tears the seal on a microscopic level and reduces its strength and elasticity. Trimming does no damage to the seal.

A more serious consideration is the damaging effects of some sunscreens. Products that contain alcohol or oils can degrade the latex.

: That cut has to be perfect with no dings or
: rough edges or it can prematurely tear.

If you're careful when you cut it (using a SHARP knife or razon blade), it's easy to get a clean edge. A continuous cut makes this easier, but it's not a necessity.

: You can get three to 4 years out of a neck seal.

That sounds about right.

Trimming seals is really not difficult. In a pinch, I've done it successfully with a Swiss Army knife and a soda bottle found on the beach.

The simple way to trim a seal is to insert a tight-fitting plastic bottle into it, the roll it on the floor or a table while you hold a razor blade against the seal. If you end up with any misalignment at the end of the cut, just trim it smooth. Small bumps are no problem, but as Jay mentioned, nicks can be. If you do find a nick in a seal, simply trim around it smoothly. The seals do not have to have perfectly even edges to function properly.