Replace your fuel filler hose! This is the large hose that connects the fuel filler neck to the gas tank. Ethanol in fuel reacts with ozone in the atmosphere to cause accelerated deterioration of the rubber in fuel system hoses. The 3rd photo is my stock BMW hose from my 2003 M3; I am the original owner where the car was always garaged and never driven in the elements. I was surprised to see how decayed the hose had become. 

This replacement exceeds SAE J30R5/J30R6 spec for E10/E15 ethanol in pump gas (no permeation). Fits ALL E46 models; coupe and convertible. Soft and pliable, easy to install. Fuel tank does not need to be drained or removed to perform this service. If you are doing any rear end or rear subframe work, you will already have more than adequate access to this part. Dealer charges about $70 for the lower grade BMW rubber hose; grab a deal here or check my listing on NAM3Forum for a better price and no tax! 

I was a 20-year M3Forum member before the site went down and original E46 M3 owner. I know the car inside and out. My handle is mpower22 (I'm also the one who developed and sells the CPV service kit to fix the inevitable oil leak), so please check my feedback; I am a trustworthy ///M3 enthusiast! 

Custom lengths available. Message me if you have a special request.