Well, when I got my first Lian Li case a few years ago, my friends smeard butter all over the case so it was really greasy, I just took some washing liquid on a piece of cloth and wipe it clean. Worked great.
I would water down 91% isopropyl to 50/50 water alcohol. there's no need for that high concentration of alcohol. plus it saves you having to buy more quicker. with higher alcohol comes higher chance of discoloration or distortion.