Corrosion In Fork Tube

Brought my forks in to the suspension shop to get the fluid changed out and they noticed the rebound needle had corrosion on it and was not moving properly. 3hrs of labour to clean up. Any of you guys experience this? I've only heard of the MX and Adventure WP kits letting in moisture, but not the SD's. I'm assuming water got in from the top cap.

My bet it's old fluid and condensation thru the tubes, not water leaking in from the top.
You keep your bike out in the weather much?
Old CAD jockey saying "Save Early and Often".
Well, you might use "Change Bike Fluids Early and Often"
Lot of guys who ride the heavy road salt roads have watched their brakes rust up.