I would really recommend that you do your swirlies as soon as possible. Go onto BMWLand UK forum and see how adamant they are about removing them. I think that i have read somewhere that the E60 and E90 also have them in but it is a modified version which is slightly larger and the flaps are plastic. When i did my E39 530d on 193k km one of the flaps was already slightly loose. I had some brass bolts and nuts which i fitted with some grey pratley puttey as well as flattening the thread of the bolts so that the nuts cannot be removed or become loose. The screws/bolts fitted quite tight and the puttey was just to ensure an airtight fit. If you do it yourself make sure that the rubber gaskets and washers of the manifold do not fall out when you replace the manifold as i remember how worried i was that i had perhaps dropped one or dislodged it when putting back the manifold. Now, three years and 50k km later it is still going strong, so i assume nothing fell out!