I had the same problem(s) for months. Checked all of the fittings, canister, valves etc. Replaced the cap. Then I started tracing the tubing from the canister, forward to the engine. Found a broken fitting on the rear of the gas tank (sorry, the pictures aren't great):
I found some stainless steel tubing ~0.180" OD. Had to drill out the inside of the broken fitting (and the fitting at the gas tank). The fitting on the tank doesn't appear to be replaceable, and a new tank is over $600.
Mixed up some epoxy glue, and applied liberally (careful not to get glue into the interior of the stainless steel tubing).
So far, so good. No idea how / why the fitting broke, but have subsequently found that the problem is not uncommon. Hope this helps for any future busted knuckles.