Just been down to Bournemouth in the sprinty, awesome ride, new clutch slave working well, also billies and kyb's feel good. had them tracked wednesday.

Seems now that there's a slight vibration that fades in and out, vibrating the steering left and right whilst driving.

It fades in, vibrates slightly then fades out-and so on.

What could this be? wheels un-balanced?

Ive checked the suspension I replaced and all is tight.

What speed does it occur? It's usually wheels out of balance, and the speed will tell you if it's front or rear.

It was above 70mph if I remember right

It does sound balance related. The fading in and out is just addition and cancellation of two vibrations i.e. the left and right wheel.

It may be worth looking for damage and bulges on your tyres and jacking up each corner to spin the wheel. This will let you look down it and see if it runs true.

In all likelihood you just need you wheels balanced.

Will go to get them balanced tomorrow. Fingers crossed.

As above does sound like wheel balancing.
Good luck

front balanced and vibrations gone.

good to hear mate