Well sir, the first time I encountered the problem, I too thought that the hose was the culprit. So I cut off a section of the OEM Merc, slick grey silicon looking fuel line and dissected it. I could have missed something, but I could not see where there was any indication of any abnormality on the interior of the line. If it was the line itself, as I had originally assumed, I would have "surely" seen variations in the surface indicating where some areas were more susceptible than others and had a different surface texture as a result.
However, the chips were arcs in nature indicating to me that either the fuel line was doing as you say or the fuel itself, was plating the wall of the hose. Course one asks the question, why just the wall and not the whole cross sectional area if it's the fuel and not decomposition of the hose? I don't know. I don't know that the hose is in fact silicon, seems to be, and don't have a list handy of what materials cause it to degrade, nor if not silicon, what it is and what makes it degrade. I do know that silicon oil makes rubber gaskets and hoses swell.
