David Blume (Alcohol Can Be a Gas) notes several maintenance cautions when switching from gasoline to ethanol.

Gasoline often burns with soot and creates varnish. Soot accumulateson the valves, piston top and cylinder walls and throughout the exhaust system. Varnish accumulates on anything exposed to gasoline. For the first few tanks of ethanol, the ethanol tends to loosen and dissolve carbon and varnish deposits. The loosened gunk gathers in and fouls the oil and filter. A good deal of it could have accumulated over the years of running gasoline, and so the oil and filter can foul rapidly. Check the appearance of the oil frequently and change the oil and filter aggresssively until this debris has been cleaned out.

Once the engine is habitually running ethanol, the engine should stay much much cleaner than when using gasoline, and the oil and filter will dirty much more slowly.

If Methylcyclopentadienyl manganese tricarbonyl (MMT) was present in gasoline previously burned, a thin deposit of manganese may have formed on some surfaces. Ethanol dissolves it and manganese accumulates on and fouls the O2 sensor. The fix is to be alert to the opportunity of fouling and replace the O2 sensor as needed.

KnottyGirlz comments in an article about ethanol-gasoline blends in boats about problems of goo and gelatinous fouling the fuel filter. The gunk is not something that precipitates from the original fuel. Instead, she suggests, it is gunk that had prevoulsly be deposited out of gasoline fuel in the walls of th fuel tank, and subsequently disolved by the newly introduced ethanol. If this mechanism is correct, then one should expect to replace the fuel filter aggressively during a transition period, and to possibly expect occassionally clogged injectors, which can be cleaned, if a clump dislodges downstream of the filter. "In all testing I read, when the fuel filter was changed as soon as the engine started to run roughly, the problem was solved. Once the fuel tank was cleared of the gunk, then the fuel filters stopped getting clogged."