We have the same thing here on white vehicule, but here it's also caused by calcium on the streets.
When I've started to work in dealers, they used a stuff called fallout gel. I don't even know if it still exists.
It was indeed a gel, and could reack very tight areas.
I remember that they applied it with gloves and had a very strong smell, so I dunno how good it was for the paint.
To help you out, you should maybe debadge your X5.
Easier to reach corners when there's none !
