There were 3 style of rear spoilers for the E24.
The first as shown on the craigslist ad car that is for sale, large solid rubber with a huge back surface.
Second is the Euro M635CSi style
Third is the latter M6 style, like the M5 with a fiberglass filler panel on top.
I have one of the early first style available for $100. plus shipping and one of the second style available, brand new NLA NOS piece from a Euro M635CSi.
Mario L.
VSR1.com
603.228.2888