Hi, hope someone can assist.

I have a Dec 2001 W210 220 CDi auto.

On occasion I get a vibration in 4th gear at around 40mph.

As soon as you slow and it drops down to third the vibration dissapears.

The funny thing is it has not done this for 2-3000miles but has the last couple of days.

Would the gearbox benefit from a flush and new fluid or is it something more sinister.

The car has done 124,000 miles and has full history, next B service due in 3000 miles time.

Any advice would be appreciated.

Thanks.