IWC "Mark X" authenticate

Hi guys, I have been a long time fan of IWC watches and caught a sight of a Mark X a few months ago. I am looking at a listing for a Mark X that has had work done. I am thinking about buying it but wanted to run by you guys first. Thanks in advance for your help. 

I dont know much about the watch, but more importantly... does the seller have a reputation for selling good condition/authentic watches?

It is part of the dirty dozen watches made for the British army...
however something does not look correct to me...
i could be wrong though...
you should always buy the seller.....

Thanks for the response. Anything specific that looked wrong to you? I noticed the movement doesnt say Swiss Made and I can't really make out the text beneath the subdial. 

It appears to be an authentic IWC W.W.W. - subtracting the case number by the M number is 18,980, which is the case for all IWC W.W.W..
However, the MoD nomenclature on the exterior of the caseback appears to have been re-engarved, I assume after having been erased in the past - the font is slightly different and the location is incorrect.  Also, the dial is a recent restoration, probabaly by IWC.

@Clepsydra, thanks for responding. really appreciate your thoughts