As eBay wouldn't have a clue that you have contacted the buyer through their personal email, there couldn't be any defect repurcussions.

And my  response was not through eBay 'contact buyer'.  It was through the buyer's personal email that comes through when an item has sold.  We had reasons for contact, and so he then also had my personal email.

(I can hear the moans from others about 'buyer protection'.  But I have to say that the people who buy from me are not concerned with that.  As I sell items that are sourced on the secondary market - the items either get to there destination intact or they don't (but they always do), so there is no 'it doesn't work, it's a fake, etc. to deal with).