When I clean one of my 7 or 8 G-Shocks, it's usually with soap and water.
On odd occasion I might use isopropyl (rubbing) alcohol.
I never would have thought of using brake cleaner on a G-Shock, it seems kind of harsh. Still, thanks for the warning.
I usually wear one of my G-Shocks in particular (DW-6600), and after a few years of pretty constant wear it looks near new.