The replacement parts for both the cover and the lower window flashing I got from the dealer seemed to be of very good quality, and of different material (hard to tell what material it was, though, based on what little was left of the cowl cover!) than the original pieces. I wonder what year BMW began using upgraded material for this? This problem seems to be largely with older e39s.
'07 335xi 6-spd 4dr, Montego blue
'98 540i 6-spd Sport, Jet Black II
'92 325i 5-spd 4dr, burgundy