[crjackson]

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I’m going to take a really wild guess at this, so please treat it as such …

The front seal of the compressor failed or the compressor was rebuilt. Either of these require the removal of the front pulley/nut. The pulley was messy, so the person who serviced it cleaned it with an excessively strong solvent, removing paint and oils. This allowed rust to easily form even with light moisture.

That’s my guess, take it for what it is …

 

[crjackson]

Sounds like a good guess. Do you know if these can be replaced? I know from previous Roush ownership that some replacement parts are hard to come by.

You certainly can replace them, but you’re on your own finding one.

If it were me, and I were bothered by this, I just remove it, clean the rust off, and repaint it (or send it out for powder coating).