How important is an authentic crystal? I took my 1950's chronometre in a few days ago and although everything is working well, the shop(Central Watch in NYC) recommended I think about switching out the crystal at some point in the future since there are hairline fissures that could allow moisture onto the dial. Any thoughts on wether this is a good idea? I'd like to keep the dial etc intact, is there any danger I should be aware of? Thanks!