Question: I have discovered that fuel has somehow flooded the inside front section of my fuselage. Any ideas as to what caused the leak and how I might go about restoring the fuselage?

Answer: 

1) Fuel in copious amounts will gradually soften and weaken some of the glues used in your model. It takes quite a bit of fuel for a long time of exposure to really attack the adhesives and it is often noticed only when the fixed firewall suddenly pulls loose or the landing gear tears out rather neatly from the bottom of the fuselage after what appears to be pretty good landing. Such separations are usually clean indicating that the fuel has eventually broken down the adhesive and under load the parts have separated. .

2) To sort this out... first of all remove your engine, power module (if so equipped) tank and servo tray. Set everything aside. Get some kitty litter (the type with baking soda in it is best) and apply a good layer of kitty litter over all the oil soaked wood. Let it sit overnight and then discard it. Kitty Litter absorbs oil as well as other stuff! Now try to get some K2R spot remover and apply that to the oil soaked wood as well. This will absorb more oil. Let it dry and brush/vacuum it off.

3) Once you've sucked up all the oil that you can, reglue all the affected glue joints. Use Pacer ZAP-A-GAP (it is amazing on oil soaked wood... no other CA bites through oil like ZAP-A-GAP) on all the joints except those related to the landing gear and the fixed firewall. Use 30 minute (not 5 minute...30 minute) Epoxy and reglue the fixed firewall and landing gear blocks back into place. Let it dry overnight and then brush Pacer Finishing Resin over all the affected surfaces and into as many of the joints as you can reach... even those that you have reglued. You want a nice seal here... over all the wood and all the joints.

4) Once you have restored the wood and joints as best you can, the next step is remove all your external fuel tubing and discard it. Carefully check the metal tubes protruding from the tank for cracks. Use a pressure test (mouth/lung pressure is fine) and see if the tubes or tank is leaking. Check the seam of the tank carefully... a seam can split weeks or months later if the stopper has been overtightened. (many folks do this to try to make sure the stopper is sealed). Overtightening squeezes the stopper longitudinally and expands it laterally. This put tremendous pressure on the tank neck and although it may last forever, after a few weeks or months, the pressure may split the seam quite unexpectedly leading to a flood of raw fuel entering the fuselage. If only the top splits, the leakage will occur when the tank is full but slow down or stop as the fuel is consumed so it may be leaking for quite a while before it is noticed.

5) Once you have the tank and tubing all checked out and repaired/replaced to ensure a pressure tight system, re-install all of your equipment.

6) Do a thorough ground test under full RPM load before flying. Firstly you want to make sure the tank is not still leaking and secondly you want to make sure that your repair job on the wood and joints has the proper strength. Do your first flight well away from people and property and inspect the tank and joints for strutural integrity after each flight. You will have to keep an eye on things for quite a while. The oil can seep out of the wood and affect a joint at a later date... your cleanup should have done a good job of wicking up any oil, but you will need to inspect frequently thereafter. If you have any doubts about the structural integrity of your model, do not fly it.