You've been going through the "to do" list of a good tune up. You've done the timing (spark), valves, and now you have to focus on the gas.
The gas part is the carburetor. A poorly tuned carburetor would fowl spark plugs and give you poor gas mileage. The fuel leak is a concern as well (think engine fire).
Start with replacing your fuel lines. Old lines can crack. Once they crack, the engine fire will ruin your bug.

Next, replace the gasket that is leaking. You may need to rebuild the carb or just adjust it. That will depend on what condition it's in. Search youtube for a how to video, there is a lot of good tutorials on how to tune your bug.
For poor fuel consumption, look at
-float leaking
-float needle valve not closing
-automatic choke not working properly
On a final note, make sure you have the original Solex 30 PICT-1 or -2. You can run different carbs, but if you have the stock carb, it'll make trouble shooting easier.