According to my chemistry class regarding accidents, once is often enough. Actually I have never met any service technician who recommends flushing the system one piece at a time. The amount of time required to take it apart and the likelyhood you will get contaminates in it any increase when removing and flushing piece by piece because it has been taken apart in pieces. Flushing does not include the compressor and the expansion valve. Since you should replace the receiver/drier anyway,say goodbye to it. Evaporators going bad with corrosion due to water and debri happen more often in Seattle than here in Phoenix and have led to evaporator replacement, especially if you park under pine trees.

Putting dye and compressed air into the system is only preliminary and I would do the next step too. An Evaporator with a pinhole leak, I've seen them, will be easy to find with dye. If no such problem exists, congrats, move on.

Yeah, our dry desert air mummifies everything. (especially rubber)