May 14 (Reuters) - NEW YORK, May 14 (Fitch) Fitch Ratings has downgraded the U.S. residential mortgage master servicer rating of GMAC-RFC, LLC (RFC) as follows: --U.S. residential master servicer rating downgraded to 'RMS4' from 'RMS3'. The rating downgrade is due to the bankruptcy filing by RFC's parent, Residential Capital LLC (ResCap), on May 14, 2012. Fitch had placed RFC's servicer rating on Rating Watch Negative on April 19, 2012. Fitch rates residential mortgage primary, master, and special servicers on a scale of 1 to 5, with 1 being the highest rating. Within some of these rating levels, Fitch further differentiates ratings by plus (+) and minus (-) as well as the flat rating. For more information on Fitch's residential servicer rating program, please see Fitch's report 'U.S. Residential and Small Balance Commercial Mortgage Servicer Rating Criteria', dated Jan. 31, 2011, which is available on the Fitch Ratings web site at 'www.fitchratings.com'.