[mikepurvis]

I think a lot of sealing rings / gaskets are meant to be single use. I had to swap the heater on my hot tub a while back and the store told me to change the o-rings on the inlet and outlet as it was unlikely the prior ones would re-seal after being loosened.

[marcosdumay]

That's common on high-pressure systems. It's not very common on diving-depth water-proof equipment.