Omega Seamaster 200 Professional - PreBond

Hello All,

I recently removed the 1438 movement from a prebond I own to do a little cleaning, I noticed that the crown does not seem to have a gasket in it, I am not entirely sure if there is supposed to be a gasket in it. I am a little worried to get water moisture and dirt in the watch, Can anyone point me in the right direction?

Thanks in advance