Apparently OP is making similar claims as RP and not backing them up, again, just like RP. Sorry, I don't care how the engine sounds with RP, I need to see how it shears with mileage and from what specs (unpublished by RP for some reason).
These engines (M50, S50) are predecessors of the more modern M54, S54 and have similar lubrication requirements are the latter, if not the same. If your e36 started their lives with dino, then fine, any BRAND name (Mobil, Castrol) oil will do fine with the correct weight mentioned in your manual. However, if you're using synthetic, my recommendation for synthetics are GC 0W-30, Mobil 1 0W-40 or BMW HP 5W-30. These are also successors of what BMW calls "special oils" in their manuals for e34 and e36 (and some e39). These have the correct HTHS viscosity of minimum 3.5 as required. Many analysis results could be found on these oils on our engines online. Just google it.
Sapphire Black MetallicNatural BrownSilver Cube
e46 330i ZHP/ZCW 6MT - Sold
Kashmir Beige MetallicSamana BeigePoplar Wood
e34 525it ZPP/Auto
M3 - RIP
Alpine WhiteTanSand High Gloss e46 330i SunRoofLess/5MT