The condenser is quite clean already - no dust or junk really noted - maybe some water staining from freeze/defrost. Will cleaning help?
As the frosting is occuring near the dryer, is there any possibility there is a restriction there?
This is a sealed system, too, running R134a. Initially I'd thought about it being low on refrigerant and recharging it, but 1) there's no service ports (was just going to use a self-tapping saddle valve to gain access for refrigerant), and 2) I couldn't really detect any refrigerant leaks.
Any additional thoughts?