Today I saw one of my scorpions, a juvenile Centruroides flavopictus, grooming itself. It looked like it was sucking on its pedipalp (pincher), but probably it was wetting it. It used its tail to spread the liquid over the top of it's body, and now and then one or more legs helped to spread the liquid even more.
I have seen this sucking on the pedipalp behavior also just before a scorpion starts eating a prey. It is holding the catch with one claw, while "sucking" on the other. My guess is that it inserts the pedipalp to stimulate the formation of gastric juices. I understand that the same juices are used for the grooming, maybe to get easier rid of parasites.
Most of the time I see this grooming happen is just after I have seen a scorpion drinking from its water dish, or with species that don't have a dish, but get some water spray now and then, when it has been taking moisture from stones or glass. My guess is that the scorpion drinks to either get more liquid for grooming or to dilute the gastric juices.