Try
www.bimrs.org for a reputable indie shop that specializes in bimmers.
I'm retired navy so I use the (currently closed) auto hobby shop at JBMHH. I do my own maintenance (oil changes, brake work, audio upgrades, etc.) there. I buy high quality motor oil that has the American Petroleum Institute (API) designation of "SN." "S" stands for "spark" (gas engines), and the "N" means the oil is designed for cars with a turbo. I use LiquiMoly. I was getting ready to change the 6MT fluid with the dealer stuff but the covid19 virus shut everything down.
PS: oil for diesel engines carry the API designation "C" for compression.