The pictures help a little.

1. You can check your fuel tank in water bath. Plug all the openings but one and apply pressure to that one opening. If you see bubbles, you have found the leak.

2. If the tank checks out, replace ALL the fuel lines and make sure they have fuel line clamps on them. Looking at the photos, I don't think the leak is in the tank though.

3. According to the photos you have 2 pressure taps coming off the muffler. The area in back of the muffler appears heavily soaked. Check that the muffler is seated properly to the engine (gasket between the muffler and engine is not leaking) and that the lines from the pressure taps have fuel line clamps on them also.

4. To try and get rid of the soaked in fuel you can try the following:

If you have a product over there called "K2R" spot remover, apply that, let dry and brush off.

If you do not have K2R, use talcum powder or corn starch and sprinkle the soaked areas with that, rub it in and let dry. Then brush off.

Either product will take several applications to get the oil out. You will not be able to get all of the oil out, but you should be able to get out about 95% (or more) of it.

Once you have gotten as much oil out of the wood as possible, seal the wood with epoxy thinned about 10% by volume with acetone. This will take a couple of days to dry, but will prevent any more fuel from getting into the wood.

When reassembling/repairing the rest of the plane, I suggest using epoxy to repair it. Epoxy is heavier than CA, but it will adhere better to the cleaned wood than CA. You will need to rebalance the plane after the repairs.

For future reference, I suggest brushing on a thined epoxy mix to the firewall and fuel tank area when assembling the model. It will prevent these areas from getting fuel soaked if a leak should occur.