doubt it not after just 4 months, ask to see bills to prove it, if he says him and his mates did it or something i would steer well clear! it is possible though, if the engine was totally out of oil, like run dry! cant really help with the engine number though im afraid, possible locations include, on the timing (cam) belt cover, on the id plate thing on the inside of the door, stamped onto the block itself ( could be just below two of the plugs) or on a plate somewhere in the engine bay. it will be in a few places anyway, the idea is to try to match a few of them up, if possible match them to the chassis number too ( it wont be the same number as the chassis number obviously but the log book or VW sales docket could help here)