This part is listed by BMW as BMW part number 11137831014 and is described as the steel/rubber gasket between the upper oil pan and the engine block on E39 M5 and E52 Z8 models.
This is an OEM S62 oil pan gasket manufactured by Elring - the original supplier to BMW for this part, as well as many other gaskets and seals. As the OEM it meets all of BMW's original design, fitment, and performance requirements and is TUV approved. OEM parts are the best alternative to more expensive Original BMW parts because they are virtually identical without the inflated price tag. This part has a two year warranty.
BMW Fitments:
5 Series
E39 (97-03) > M5 (00-03)
Z Series
E52 Z8 (00-03) > Z8 Roadster (2000-2003)