...if you wish you could replace the centre covers with the later and more desirable (it seems) "throwing star" covers. This is what I did. If they are a good deal in U.S. dollars I suggest you buy them as they do not come up for sale very often - even in the U.S. and they are O.E.M. (original equipment manufacture) made for the ///M5.
Not many people know this but these ///M5 wheels made for '88, '89, '90 M5's, the spokes at the centre (the black painted part in those Ebay photos) were cast approx. 5mm thicker than the spokes on the '91 and on M5 wheels fitted with the "throwing star" centres. This means that to fit "throwing star" centres to early model wheels you need to machine the centres approx. 5mm so as to have the "throwing star" centre sit properly. (ask me how I know)
regards
Phil