I ask this question at the Pentax / Hasselblad service centre in Halifax.
They use a 60/40 solution of Methanol & ether; what a greeting walking through that door.
For home use they recommend 50/50 solution Methanol/water; a few drops on a lint free cotton cloth, wipe the lens let it dry.
A bulb blower ( little rubber bulb with a nozzle) is fine; but first wash it out with soap and water. Powder is use to coat the mld when they are made and not cleaned out after production.
Brushes not recommended, micro fibre cloths very good for the service centres' business not the lens, grit can get caught in the micro fibres.
Anyway that was the advice I received from a person with about 40 years of experience.