DIY cleaning of 70-200 f/2.8 L IS II - experiences?

I can detect the tell-tale low grinding sound from my focus ring on the 70-200 f/2.8 IS L. Not sure what happened, but my guess is that a speck of mud first fell on then dried on the lens during a shooting the other day allowing it to "creep" into the focus ring.

Now the question is if I should try to pry the lens open and remove the sand trapped inside - or send it to the ridiculously expensive and slow - Canon service centre here in Europe. I do not expect that the sand has settled inside the lens itself. But I will need to take off the focus ring.

Would like to have advice from those who have opened this lens themselves or other Canon zoom IS lenses to fix a similar problem. Is it rocket science or only a question of careful mechanics?

Let me add, that if it involves fiddling with the glass elements inside - its nothing I will attempt myself.