I have an R56s N18 manual transmission (78000 miles) that is having an issue with 6th gear.
The shifter tries to pop out of 6th gear when I accelerate. It also seems to jump out of 6th randomly when I drive on the highway.

I can see the gear **** creep towards neutral when I accelerate in 6th gear.

Anyone know if there is a quick/cheap way to fix this?

 

Check the coolant pipes under the hood. They might be in the way preventing a full engagement.

 

Do you have an update for this packman86?
I'm in the same boat and the problem is a bad driving habit (running on low revs with 6th gear engaged).

In my case the 6th gear and the synchro (5th - 6th) are worn

 

Took it the the shop and was told I need a full transmission replacement. Either a used transmission or brand new one.

Either way, its going to be expensive and I'm just going to run 5th gear instead.