Buy a new stringer or a Wise tension head.
I do have another idea though. There are paint brushes that are used to paint in conners and around doors and windows. They have a thin replaceable pad. Don't know for sure but those pads with the little bristles may fit between the plates and is soaked in alcohol they may clean the gunk out is you clean both surfaces real good. Not say they will work but may be worth a try.
I'm not saying you can't take the gripper apart as I did that. I'm saying it is not easy and I would not recommend it. There are two large plates the sliding grippers slide through. Make sure you mark all four pieces so they go back together right. While they are apart you can clean and inspect the surfaces that contact the string. When I put mine back together I had to lay down the left side large plate with 8 bearings in each grove. They lay down the left slide with the springs then the right slide with 8 bearings in each grove. Now you can't screw it together because the whole thing has to fit on the tensioner. Pick up everything making sure nothing falls out line up all the holes with the holes on the tensioner. Tighten the screws and check your calibration.
You could also go to the for sale section and look for another tension head. They may be someone who bought a Wise and thinks he will never need the old lockout. Maybe there is an old lockout out there with another problem and you can cannibalize it. You never know.
EDIT: Here you go place an add here
EDIT: Another quick search of the For Sale or Trade turned this up