the rockman 108.9 is actually a try all if you scrach the black paint off the lock ring you will see the logo. the ring is welded so you cant easily tighten it. i am currentley trying to get mine appart as it feels like there is gravel in it. if you have ever taken a freewheel apart befor i suggest you get the lock ring off the back. it is welded so will be hard (i carfully cracked the welds after scoring them) and have a look whats going on may be one spring thats damaged or something simple. remover the faulty bit and put it back together, you may loose some engagment but a 96.8 instead of a 108.9 you wont notice the loss
if you dont want to try this just buy a new one its not worth the risk mate and i cant ride properly when i have something like that in the back of my mind
DO NOT over tighten the lock ring it wil cause you problems the freewheel will be stiff and then the lock ring wont stop coming loose