Scart Leads

Can anyone tell me how important scartleads are.
My DVD picture is flicking from light to dark when watching a disk and there is a very faint band drifting across the screen on the hard drive.I have my jvc drm 20 DVD Harddrive recorder fed through my video using bog standard scarts leads.When the picture is fed directly there is no distortion.I dont think there is any fault with the video so is it the leads?
How much should i spend on leads, i dont need great quality, just a consistant picture.
If you can help,