The answer as far as MS is concerned is a resounding NO. An OEM is for 1 computer only and when that computer no longer exists then neither does the OS. From your point of view, even though you have upgraded the computer that the OEM was on, the computer,technically, is now defunct. I do not know, however, if the buyer could get round this by telling lies. Why leave yourself open to legal action for a few pounds?, you had a years use out of it.