I'm in the process of changing my supercharger oil. I ordered a kit to do this online, but noticed that instead of GM Supercharger oil 12345982. They sent me very similar looking bottles of GM limited slip additive 88900330. Is this the same stuff? I've put it in my supercharger, but haven't put the supercharger back on the car.

 

No they're not the same or they would carry the same GM product number, 10-4041 for the supercharger oil. Sounds like maybe they shipped you the wrong stuff by mistake; they do look alike but a quick check of the part number should have prevented them doing so.

Would dump, flush with brake cleaner, allow to drain / dry then refill with the proper oil, available at many vendors.
https://www.ecstuning.com/Mini-2006-...ercharger_oil/
https://www.outmotoring.com/MINI-Coo...2007-2008.html
https://www.pelicanparts.com/More_In...=c&SVSVSI=4500
https://www.summitracing.com/parts/n...5982?rrec=true

 

Yep you need the 12345982 stuff.