Left side crank case cover? I had one of those too. I wasn't doing the work at the time, but I think an impact driver did the job. If you get it out without any other ill effects, replace with stainless hex to avoid future stripping. I still need to do this, but I am going to wait until I have to take it off again, which will be in the near future as I have to replace my clutch cable. Verify with the impact driver solution with someone else first though as I recently tried that on my tachometer cap assembly and broke it in half.
