Using Prolong Oil Additives in the * Series

I have used Prolong Oil Additive which I understand comes from the States in three of my other vehicles, namely a Mazda Pickup and 2 Volvo Estates
The Mazda stopped smoking and the performance was notably different
But !!!! I see in the 840 Manual that I am not to add any additives to the oil
Can anyone tell me why and if it willl do any damage if I did add Prolong to the BM
For further info on Prolong see

www.prolong.com

Thanks for your help

Chootspah

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Bump

Good quality oils don't need any addatives. My guess is that BMW (the fine, well engineered car that it is) doesn't want any foreign addatives floating around in their engines. Most of that stuff is a gimmick any way, and some can do more harm than good.
Amsoil synthetics are European certified and have outstanding lubrication qualities. Mobile 1 is good too (I use both brands).
Use a good oil and you don't need addatives.