A sensor transportation apparatus to convey a sensor assembly through a bore comprises at least one engagement structure to connect the sensor transportation apparatus to the sensor assembly, one or more wheels each arranged to rotate on a bearing about an axis of rotation substantially perpendicular to a longitudinal axis of the bore in use, and a lubrication system.

The lubrication system comprises a reservoir with an elastomer diaphragm, with an exterior side of the elastomer diaphragm subjected to an ambient bore pressure.