Is this a Seamaster 300 (vintage or Watchco), or a Seamaster Professional? Your title says "SMP300" so I'm not 100% sure which watch it is.
If it's the SM300, then as dsio states the crown seals on the case tubes are notoriously tight, and there is really nothing that can be done to fix it, other then using it and having it wear in.
If it's an SMP modern watch, then something is wrong - crown should not be hard to turn.
Cheers, Al
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