Based on careful reading of the Turner Motorsports advertisements above, it seems they're implying that only the "early M50 & M52" engines 'may' have had plastic impellers - after which BMW quickly switched to composite impellers (note: the aftermarket has always had the metal impellers).
Assuming this statement by Turner Motorsports is true, then the only remaining question to answer the OP's question is the following:
QUESTION: What E39 models used the "early M50 and M52" engines? (i.e., these would have had plastic impellers originally, but which would have quickly switched to original composite impellers.)
Please read the suggested threads, where the best always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks
& How to easily find what you need
Last edited by bluebee; 02-04-2013 at 07:48 AM.