washing
Just traded my 19 month old GSA that had covered 22k miles. I only ever washed it with a pressure washer. I think the agent washed it a few times with soap etc after servicing. It had one problem which was the aux light switch that needed replacement after about 20k miles. This was weird because it was switched on when I took delivery of the bike and left in that position until I traded it! I was sympathetic with the washer and just used it to remove the dirt in a controlled manner. When I took the bike in, the only areas of compromised brightworks were the areas that BMW acknowledge and replace under warranty (alternator cover, final drive etc)
The analogy I can offer is that in the right hands, an angle grinder can be a great tool and deliver very good results. In the wrong hands, the angle grinder will destroy the subject. The same applies to a pressure washer!