Lubrication film thickness monitoring between moving contact surfaces within industrial machinery is of great research interest because it is linked to the efficiency and rate of maintenance of the machine. Ultrasound reflectometry shows potential within this field of research, primarily because the ultrasound transducers can be conveniently implemented in operation-ready machinery. In this article, the lubrication film thickness inside an operational radial piston motor is estimated using two adaptive ultrasound reflectometry methods. A new Gaussian random walk based adaptive ultrasound reflectometry method is compared against the existing layer phase-lag method with adaptive Extended Kalman filter based calibration. It is found that the new method proposed gives less noisy and more accurate lubrication film thickness estimates, but it is more difficult to tune. It is found that both methods can detect the significant lubrication film thickness dynamics present in a radial piston motor, but they need further investigation regarding their robustness and reliability.