BMW have an underseal that comes in aerosols but it's not as good or the same texture as the above mentioned products. I'll see can I dig up a part no.
Nobody is going to notice or argue if you use the above mentioned. The original stuff is 20+yrs old, who knows what they used or where to get it?
4x types of underseal/stonechip here with part no's: http://www.bmwsteelart.com/webetk/pa...3_0498&LA=enAA
I've used #2 while it's grand I would only really use it for small area's and patch ups. It's not quite the same effect as originally on the sills,