I remember reading that Stevie recorded a demo (or whatever) of Sara in Dallas with Gordon Perry. She also said that she played Sara on the piano everyday for months was the rest of FM was walking in the studio to make them interested in it. Finally, in the end the "Cleaning Lady" version, one or more people (someof which are Stevie) are singing harmony and the coices do not soumd like CM or LB. To me, the voices sound like Stevies back up singers
In the end, I think it is FM on there as it just sounds like them.