Yes, it's cheap insurance. I replace the "O" ring gasket on my Tiger Shark every 2 years. I would not use an old "O" ring gasket even if it is unused in a box. They deteriorate with age, not use. Leakage of water is not covered under Tesoro's warranty and why risk loosing use of your detector for such an inexpensive part. I use Trident (brand) Pure Silicone Grease (available at dive shops or on Amazon) on mine to a clean "O" ring and I clean the groove on the detector with lint free gun cleaning patches in a Q tip stick with the cotton cut off and removed. Remove and clean the "O" ring and clean the groove every time you open the machine and apply the silicone grease very lightly to the "O" ring only.
