Another thing you can try - which has worked well for me is a bit of homebrew plastic welding.
Usually these leaks are splits rather than holes, really, the only way to find them is to pressurize it with water and see where it's leaking (both sides), you then drain it and make sure there's NO water in it before going on to fixing it. Now cut a sliver of the solar panel off from an outer edge, this will be your welding stick, use a plumbing torch and a knife, heat the knife, touch it to the cracked are while holding the "stick" to the exposed side - essentially you're melting both the panel's top surface and the stick at the same time, the stuff from the stick should flow into the melted upper layer of panel, once enough it on it, run over it with the knife and it should bond the new material to the panel - I've saved several traces that way - with every trace you plug, you lose heat gain, so the longer you can get away with doing this, the better.
If you mess it up, go to the plug method - really, you have nothing to lose to try and fix it.
I have tried every glue or epoxy possible to overlay cracks with no success - even marine epoxy, so don't waste your time and money on that method - it just doesn't work.