I may be reviving an old thread but I have been having issues myself with these metal gas tanks on the Apollo 250rx leaking from the gas cap. I found a site in the Netherlands that sells just about every part you can imagine for these bikes. I took a stab and just ordered a new plastic tank and cap from them today. Will repost with pics, total pricing and shipping specs once I receive the tank.
http://store.orionmotors.nl/