Being a rookie with these cars, it is a little confusing to me. Real OEM lists (at least) 3 PNs for the windshield rubber (Sealing Frame). I checked a 2800 Bav, a 3.0S Bav, and a 3.0Si.
The 2800 Bav specifies PN 51311809676 for the sealing frame (6/69-7/71) and PN 5131180028 for the decorative frame bottom (no year range).
The 3.0S Bav specifies PN 51311823080 for the sealing frame (7/71-7/74) and PN 5131180028 for the decorative frame bottom (no year range).
The 3.0Si specifies PN 51311828235 for the sealing frame (9/73-7/76) and PN 51311808247 for what they now call the decorative strip (9/73-2/77), but it is called out with the same reference number in the illustration as the decorative frame bottom for the earlier cars. It also lists 5131180028 using the same reference number in the illustration and calls it the decorative frame bottom (no year range)
Sealing frame PN 51311809676 and PN 51311823080 are showing with a price like they are still active parts. Sealing frame PN 51311809676 is showing as ENDED.
My GUESS on all this is that the earliest sealing frame (5131180976) was superseded about at the introduction of the 3.0 Bav with 51311823080 but still took the same, early, narrow decorative frame bottom (5131180028) and probably used the 51311823080 sealing frame if a replacement was needed. Around the time of the face lift, that sealing frame was superseded with 51311828235 which now took the wider decorative frame bottom (and now called it a decorative strip) 51311808247.
The overlap on some of the year ranges is probably due to different parts used on cars for different countries, and a phase in of the newer parts over some period of time. It doesn't appear that BMW had "model years" then like we had (and have) in the US. My car (for example) was produced in 7/71 but was sold new in 1/72. It has the painted rear panel and brushed stainless switch panel like a 1971 2800 Bav, but because of the 3.0 motor and 1/72 sales date, was titled as a 72 model year. If produced by a US maker, this car would have most likely been called and titled a 1971.
I hope one of the experts here can chime in with "the real story".
