Originally Posted by tagesk
BMW doesn't make oil, so what do you mean with "factory oil"?
Any fork oil will do just fine.
Realoem.com is a BMW-specific parts catalog for cars and motorcycles. There is a part # for telescopic fork oil. P/N 31427652283 for 5000mL, and 31429062158 for 1000mL.
I have not checked to see if these are good numbers with the local BMW shop yet.