From another forum - but I know someone who's been stitched up.......this should be a sticky because there's a rip off artist on the loose! The more folk that are aware of this scam, the better.
"Looking around four breakers in the Oxfordshire/Gloucestershire area last week, I noticed that every 320i and 520i had it's inlet manifold removed - about nine cars in total so no coincidence. It seems that some crafty individual is removing them, and selling them as M50 2.5i manifolds. To the untrained eye they look identical but there are a couple of ways to tell apart from the added fatness of the 2.5 runners - one is the diameter of the inlet port (which I don't have at the mo - can anyone assist?), and the second is the part number cast in - on these it should end with 2.0 on a 320i/520i manifold but it's small lettering and would be missed if you didn't know exactly what you were looking at.
The 2.5 manifolds are now getting incredibly rare and there are loads of 2.0 ones about, just waiting to be removed and flogged to some poor unsuspecting sod. It's worth making this post a sticky IMO - you'd be really pissed if you paid £100 for 50p's worth of plastic junk".
A mate of mine bought an M50 manifold on Ebay a while back, and it was a 2.0 one......