  We report 75As NMR measurements of the spin-lattice relaxation in the
superconducting state of LaFeAsO_(0.9)F_(0.1) and As-deficient
LaFeAs_(1-d)O_0.9F_0.1. The temperature behavior of 1/T_1 below T_c changes
drastically from a T^3-dependence for LaFeAsO_(0.9)F_(0.1) to a T^5-dependence
for the As-deficient sample. These results, together with the previously
reported unexpected increase of T_c and the slope of the upper critical field
near T_c for the As-deficient sample, are discussed in terms of non-universal
SC gaps in Fe-pnictides and the effect of As deficiency as an exotic case where
nonmagnetic 'smart' impurities even stabilize an s+- wave superconductor or
within a scenario of a disorder-driven change to s++ superconductivity.
