It all depends on a few factors in terms of value like does it have a transparent red back or is it black? MKI and MK II modules had the red as well as red slider switches and the MKIII and IV had the black.However some modules that were upgraded to a current module still had their original sliders installed on the new module.
More impotantly is their any evidece of the seal where Lexan top and bottom meet being violated? Does it show any visual internal corrosion damage?Some units went into self destruct mode and this could be an issue on value.
Normaly I do not recomend opening the module for any reason, but if you are extremely carefull and have experience tinkering it may be necessary to open it up for the chance at fixing it. However once this is done the original five digit serial # is no longer authentic and should NEVER! be sold as if this is a normal repair or improvement. For one the watch will no longer have an air tight seal, thus no longer being waterproof
or shock resistant like it would be at it,s original state with the trade seceret gel comprising the entire inside,not just the battery area as some have been led to believe.
When my father said you will never replace batteries again in his adds he meant it for more reasons than 1.
You can send me a pm after you check it out.