Multispace roof bars mounts

[ozzo486]

Hi I have an 09 Mulitspace. I've bought roof bars with mounting feet. There are 3 M8 bolt holes on either side of the roof. I presume someone had them fitted previously and have not replaced the caps. I've had to run an M8 tap to clean up the threads before I could fit them. This worked on three of them but the last one it didn't. The whole of the round mount with the M8 hole in the middle is spinning.
Anyone had this problem and know how to rectify?

Thanks