serviced loads of forks for people in a professional environment.
Seen a LOT of worn stanctions.
The comment about caustic cleaners is spot on, there is always corrosion with the wear, and the old oil kinda smells soapy.
I even serviced a fork where the oil smelled like off milk, and looked like it! The stanctions were lovely and smooth. The owner was amazed by them after a service, they actually had damping!
i have seen forks where the seal has dried out to the point that the rubber is cracked! We all know what a plastic gear cable housing will do when rubbed against a frame, wear it away. This is exactly what happens when seals dry out too.