Departing neighbours leaving boundary issue problem? Any ideas?

I moved to my home about 8 yrs ago. Within 2 wks neighbours had built a wooden extension to their own property, only telling me after the event that they had encroached two inches onto my property with the concrete foundations. Didn't fuss at the time but they put in inadequate guttering and it has flooded my side path regularly. Didn't want to fall out with neighbours over trivialities but property is now sold STC and I can't get them to confirm if they let the new buyers know about the encroachment and they are not prepared to do anything about the guttering as he now claims the path always flooded. I never had the chance to know that as their build went up when I had only just moved in so I can't confirm/deny their assertion. Their move is full of the usual drama, marriage break up and family troubles which I'm sorry for but it is none of my business. What's my best course of action? The estate agent's are useless and the current owner told me this evening that he had sent in the paperwork saying that there were no outstanding issues which leaves me in a quandary. Should I be consulting a solicitor? I don't really want to start things with a new owner on a bad footing or leave it with the departing owner with bad feeling but I have put up with this water problem for years and rather resent the way it's been handled. Suggestions anyone