Alumina is easily stable in alcoholic fluid and you should be able to get a great stable fluid just by adding your particles to the fluid and sonicate for a long time (2-3 hours). Remember to cool down your nanofluid or you will evaporate all your alcohol. If you want to add a surfactant, you should consider add a few drops of triton to a 50ml nanofluid. It should help you have more stability. Let me know if you succeed making your nanofluid. Good luck!
Florian Carle suggested good points. In nano particles, the exact method application matters a lot. e.g. the time, mixing order and mixing time etc. I hope you will get your desired stability after following the above suggested steps. Regards