If 100LL was perfick then I'd admonish you. It (100LL) may be as it leaves the refinery (FAME excepted) but the conditions in which it is stored and delivered at your local field may or may not leave much to be desired.
If you use up the tank full of MOGAS regularly I'd not be too concerned so long as adequate checks for water are carried out before each flight and you have ensured that the fuel system delivering the liquor to the donkey does not decay as a result of exposure.
Dave Wise at the LAA was an authority on this.
Sir George Cayley