Here's a site to help you. Pretty interesting. In the 50's they started a date code that was added to the back - L3 - is 1953. Click on the links on the site.
Determining the Date of Bulova Watch
United Kingdom: Bulova UK Ltd, 8 Woodshots Meadow, Croxley Green Business Park, Watford, Herts, WD18 8YU United Kingdom, phone +44 (0) 1923 226936 or +44 (0) 1923 236576, email [email protected]
contact the service team directly
It is possible a tiny gasket is inside the tread... needing to be REPLACED before proceeding.
First check to see if it is a "left-hand" or "right-hand"
threaded CROWN... Then check that there is no damage to the STEM or the CROWN... You will need at least a 10x (power) jeweler's loupe to see that.
If you have any damage... A watchmaker might be able to dress the treads and save the ORIGINAL PARTS...
Else you are probably looking at replacing both the stem & crown...
put make model and any numbers into google.
or put more info on here.
or if you are asking were is the number on the watch you will have to take the back off it and see if there is a number in there.