Do not remove any lever from the rear shock! Various important parts nestle behind the lever and removing the wrong bit results in an expensive service at your favourite suspension specialist.
I’m not saying that it’s impossible to remove the lever without consequence – I’ve not actually tried – but the above is a summary of what I was told by Mojo when I called to ask.
To clean behind the lever, use a spray can of compressed air and a toothbrush.
Edit 2: It might not actually be grit that’s gumming it up since the lever can also stick due to other reasons, which is covered under warranty.