Guibo bolts are a pain in the arse on these cars.

For a start, you have to get the car high enough to get a fookin massive breaker bar in under the trans tunnel... and then you have to devise a clever method of locking the back bolt on the guibo.

When I did it for the clutch change, we used a breaker bar, impact socket and appropriately sized spanner. Fit the spanner over the back bolt, and brace it against the body work (With rag wedged between please! Dont want to chip paint off) so it cant go anywhere. Get the breaker bar on, and if the space is limited you may need two people to get the breaker bar to move properly I fortunately had help when doing this. With me on my back, and a friend ragging on the breaker bar from the side they came undone quite easily - I could imagine a lot of skinned knuckles and swearing if you try this on your own.

If I were you, I'd back them all out and inspect, if two have gone you may find the others are on the way! If they're 'new' bolts with the guibo, I'd be highly suspicious of their steel quality - it could be a bad batch and a matter of time till you get caught out again! If you're sure they were new, I'd get a complete new set from a bmw dealer, thats the only way you're going to tell they're to spec...

Cheers,
Andy