This is a genuine BMW trap circuit, part number 65 24 1 387 803. The number stamped on the part is 65241387803; BMW's catalog files it under the short number 1387803. You will find it on our Instruments & Electronics shelf, under Other Audio, Navigation, Electronic Systems parts.
It fits the E36 sedan and coupe (318i, 320i, 323i, 325i, 328i and M3, 1992–1999), with the M40, M42, M43, M44, M50 or M52 and other engines — and the European-market versions.
BMW draws it on the Single Parts F Rear Window Antenna (65_0049) diagram. It weighs about 27 g (under 0.1 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.