My 2007 MuSL has had chronic headset wobble from two sources. First, the white plastic clamp adjustment bolt loosens on its own, but locktite fixes that for a year or so. Second, I've had to replace the headseat bearings twice. The first time, I let it go too long and the bottom sealed bearing blew completely. It made for a very sloppy ride, downright dangerous. The second time a year later I caught it sooner. Both my local bike shops had the right bearings in stock, even the one that doesn't carry folders. Crane Creek 1 1/8" Z6 Z2 or something like that.
Watch those headsets! You can distinguish headset from handlebar lock by tightening down the handlbar clamp, popping the handlebars back up, tightening in the front brake and looking for wiggle in the headset area.
Good luck, all.