we have noticed over the last few weeks the hot water is not as hot as it should be. So I went up and unscrewed the release valve and put about two liters of antifreeze in to the system. Then I noticed a small puddle on the roof at the corner of the panel. Iit's leaking very slowly . Has anyone tried to fix a leak like this with one of the chemical additives and did it work or have I got to go and order a new panel. This one is maybe 12 years old.