Ray, you must be polite but firm with this customer. Point out to him that there can be no association with a job that you did in Feb., and the problem about which he is complaining. Tell him that your cousin's best mate is a building contractor who has seen this problem scores of times, and that in every case the damp emanates inwards from the wall to which the plasterboard is attached, through the adhesive blobs, especially if an inferior adhesive has been used. Also, educate him to the point that, had the damp originated from within, the plasterboard would be universally damp, not just in blobs. That done, leave it with him, assuring him that should he want any further help from you, all he has to do is call. Best of luck with this awkward situation. Mike