Yes, it is true. Older rubber componets do not hold up well to exposure to alcohol, be it ehtanol or methanol. MTBE is also very bad for rubber (not used anymore). Newer rubber materials are resistamt to it, but not all carbs/feul pumps are being made/have rebuild parts that atre made with the new style rubber. Ethanol and methanol is also corrosive to metal components, especialy aluminum, though I have been told that it's only a real issue if a vehicle sites for an extended period of time with out use. Rod and Custom recently did an article about this subject, with listings of what popular vintage carbs have ethanol compatible parts available.
Others will probably chime in on this.
BTW, we run 10% ethanol here, so far, I have not had any adverse problems with my feul pump of re-built Holley carbs.
