Am having trouble with the rear driveshaft coupling on my 1990 sierra cosworth 4x4, has got a few cracks in it and am trying to find a replacement but has been 6 months and still no joy, have found a superseded part from ford but does not have the centre bearing of the old one and have heard stories that if not there will cause a vibration which is what I have already.

any help would be greatly appreciated
thanks hadyn