I had to go grab my 4/98 E39 528 (M52 engine) manual to check, out of interest.
In the writing section, it indicates that API SH, API SH/CD or API SH/CE is required quality.
In the graphic, it indicates API SG Energy Conserving II (what??? THe more detailed specs I've ever seen indicates LL-98, LL-01, ACEA A3. Energy conserving is never going to reach ACEA A3)
The graphic indicates 5W-30 10*C and below. 15W40 -10C and above (with a cautionary note that below -10C 15W40 may cause the engine to become hard to start and to use special lubricants!) On the other side indicating all ranges from below -30*C to above +30C to use "Special Oils* - most preferable"
The footnote* says "Special engine oil individually approved by BMW (low friction lubricants). Contact your BMW retailer for details". I guess this is LL-98.
Over its life this car saw a Pennzoil synthetic 5W50 (Penzane days) for the first three years as the choice of the indy who was the friend of the original owner. I used M1 0W40 for a couple of years and GC for the rest. When ARXing or just this summer for the heck of it (and 1/3 the cost of GC) I'm using XD3 15W40 HDEO.