I built one of these and I was lucky, I never had any leaks! Do you have your fence post placed properly above the reservoir? If moving things around a bit doesn't help, you may be able to do what I had to do in my DIY cloner. If you take your lid off the reservoir, you can attach a piece of plastic sheeting all around the inner edge of the lid. You only have to make it a few inches long, just make sure the plastic wraps all around the lid and overlaps itself a bit. I used a 4ml plastic sheet that you can get at any home improvement store and I attached it to my lid with gorilla tape. I was worried about the tape holding, but I have never had an issue with it. I had a lot of issues with leaks in my cloner until I did this, have not had an issue since. Good luck!
Also, that is an amazing system, I have had great success with it. I studied his threads for a while before I started growing. I think you will be happy with your decision of systems.