Unlinking synced audio

Hi,

I just started working on FCPX and I've come across plenty of problems so far, mostly now resolved.

One problem I can't seem to figure out:

I am working on a project with 2 cameras. Both cameras have internal audio (that I do not wish to use).
Additionally there is audio from an external source.
Someone went ahead and synced all the audio already, so all clips and external audio are in sync on my timeline.
However, I came across one clip that is not synced just right. I figured out where it needs to move in order to sync by comparing the wavefronts (and listening in)
My problem is: when I try moving the clip, the synced external audio comes with it. What I basically need is an un-link of the two sources (formerly a simple push of the "L" on the keyboard). I've tried all sorts of commands like "detach audio", "expand audio" and "break apart clip" - the clip remains locked to the external audio.

I must be doing something wrong, and surely the solution for this problem is simple and quick. But I just can't find it!

I hope someone out there can help.

Thanks so much!