A method is disclosed for replacing grease in a main bearing of a wind turbine, the main bearing located in a housing and the housing having least one cover plate. the bearing cover plate is removed from the housing, grease is manually removed from the main bearing, and a flushing cover is installed on the housing in place of the bearing cover plate. The flushing cover has at least two parts, the parts fitting around the main shaft, and each part having a seal so that when its attached to the bearing housing, the flushing cover forms a seal with the main shaft. The flushing cover has holes allowing access to the main bearing, and a solvent or oil is sprayed via one of the holes onto the main bearing to remove grease, the remaining holes being sealed by a removable plug. Solvent or oil is pumped out of the housing via a port at the bottom of the housing or flushing cover. The process is repeated for each hole, and the flushing cover removed, the main bearing packed with grease, and the bearing cover plate re-affixed. The spraying step involves pumping solvent or oil from a reservoir to the spray nozzle, and the step of pumping solvent or oil out of the bearing housing involves pumping solvent or oil to the reservoir via a return hose. This means that the solvent or oil is recycled during the replacing of the grease. An apparatus for flushing grease from a main bearing of a wind turbine is also described.