My latest attempt at replacing a crystal on a 7002 went horribly wrong resulting in a badly knackered nylon gasket, which are now rarer than hens teeth. Right, lets try something different.
First attempt. Obtain a 7S26 gasket. This is 0.5mm smaller than the original but if you carefully stretch it should work, fits nice, press the crystal in…… ARRRGH! I broke the crystal.
Second attempt. Obtain a 7S26 crystal (Seiko part no. 315P15HN02) and a Sternkreuz L325 gasket. If my calculations are correct it might work.
Happy to report that it fits like a glove, nice & tight but easier to seat than the normal set up. I can’t confirm if this is watertight as I don’t have the test equipment & my diving days are far behind me now. The end result looks much the same and also opens up the possibility of using 7S26 sapphire crystals, which are easier to obtain than 7002’s.