s3 swb, what speedo cable

Put a new speedo cable on my s3 swb, i noticed the hole to the speedo drive on the gearbox was square but the cable was oval? it works for about 50miles then gives up, if i unscrew the cable and refit it, it works again? then gives up! have i got the right cable? (the speedo works when i put the cable on a drill), stock 4 speed box, old oval cable worked for two years no problems?

dont bother mine worked for a week then stopped you wont get a pull they dont go fast enough lol

35mph in a 30! broke my heart, traffic school! I'm selling her on but i want to keep my sat nav,

ouch there hope for mine then lol good look at drivin school mate