I have a small die grinder ,uses 1/8'"shank tools. Also a bunch of diamond discs and abrasive discs 1/2" dia and carbide bits. Between them I would grind opposite the gap and then pick it out or if necessary grind in two opposite places. The discs are only about .020" thick. The carbide burr would leave a groove in the aluminum housing but that won't hurt any thing.
It wouldn't hurt to make a flat mandril to tap the ring a few times to help break the bond before you start. Those 1/8" tools are dirt cheap as is the grinder I think at HF it was $18.
if its against aluminum I would just heat it with a torch, pour some heat to it, it should burn the corrosion right out and soften the clip so it isn't fighting the so hard. unless there is something tight against it that would melt that would be my first attack anyway.
Nitric acid pickling gel to remove rust stains from stainless also contains hydroflouric acid.........so do be careful ..........the old boss at the refinery used to say "Hydroflouric acid will neutralize on your bones."
It looks like there is some type of bearing sealer on the snap ring. Like Idacal mentioned put some heat to the part. If you can heat the outside of the part where the snap ring is. That will help some of the sealers release on the snap ring. Then take a small punch to one of the hole in the snap ring and tap on it with the punch. Some time it will just cause the snap ring to spin, or it will cause the end of the snap ring to pop out of the groove. Then just work it around the bore, be sure too put a small screw driver behind any part that comes out of the grove. If you walk the screwdriver around you can get the snap ring out, just be careful to not damage the part.
Also make sure the tips of your snap ring pliers are still nice and sharp. If they are worn any find a better pair. It what I did for over 35yrs rebuilding automatic transmissions when I had one like that stuck in a groove.