R&R Tensior Shock, Please Help

Hi, I'm really stuck. I'm trying to replace the Tensioner Shock Absorber on my '93 190E. The bottom bolt comes off no problem. the belt idler wheel
comes off no problem. then - what appears to be a torx T30 bolt - will absolutely not come out from the collet in top of the shock absorber.
Looking at my new shock, however, I note that the collet is threaded AND there is room for a nut at the end. that means, the nut will act as a 'lock nut' .... it's recessed though. In addition, the torx head does not have a particularly deep recess for the tool to fit into (on purpose maybe?) to get a good grip and therefore will strip easily.
I'm guessing that I'm missing something and have reassembled everything.
any ideas? thanks
cheers, guenter
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