An oil transfer unit 1 has a rotating part 19 extending along an axis 7, a stationary part 18 provided with an oil mouth 29, and a floating part 20 coupled to the stationary part 18 in an angularly fixed manner and with a defined freedom of movement; the floating part is provided with a cylindrical surface 87 fitted onto an outer cylindrical surface 88 of the rotating part 19 in a non-contact configuration, with an annular groove therebetween to put the oil mouth 29 into communication with an inner chamber of the rotating part 19; both sides of the groove are sealed by oil films at a radial gap between the cylindrical surfaces 87, 88 of the floating and rotating parts 20, 19; the unit has a plurality of recesses, which are delimited outwardly by the floating part 20 and inwardly by the rotating part 19, are arranged on the opposite axial sides of the groove 90 so as to locally enlarge the radial distance with respect to the radial gap and are inwardly closed by the rotating part 19.