An ex-RN Sea King pilot tells me that it was SOP to flush turbines to get rid of salt deposits after flights at sea.
Park on deck with turbine at idle and spray clean (non-saline) water from a hose into the intakes using a circular 'rose' on the end of a long stick.
OK - far from ideal but as a means of cleaning the turbine apparently just as effective as flying through torrential rain. Which bit(s) got cleaned is unclear but apparently power went up and temperatures went down as a result.