My 75 hadn't been washed for about 10 days, and was looking quite grubby, after 1000 miles of motoring. Gave it a quick rinse underneath, and in the arches, at the jet wash, and got the worst of the salt off the panels, though it still looks a bit grubby.
Here are some photos of how it was looking until I went to the jet wash. So, how grubby is your 75 looking?