This is a really easy swap, heck I even did it without smashing my watch!
When I reassembled it, I put a tiny wipe of grease around the inside and outside perimeters of the crystal where it seats against the case, then pressed the crystal retaining ring back down firmly. The ring went back on much easier than it came off, and I like to think the grease offers a bit more water resistance than would otherwise be there. And lo these 3 hockey seasons later, and dozens of practice sessions, the crystal hasn't knocked loose or sprung a leak.
(@Freddy, I know... I know... I need to do it with the gen. It was eaaaaasy to tear the MBW apart, I tread a bit more carefully with chocolate dials.)