Rust on Rubber
Rust Stain on Rubber
Here's a close up of the worse of the two bushings in the vibration damper weight shown in the above link for cast iron. The rust is caked on pretty heavily and should present quite a challenge for the liquid to remove AND not damage the rubber. Click image to enlarge.
Rust Removed, Rubber Safe
As you might have already expected, the Rusteco Liquid did the job, completely removing the rust and saving the rubber. The cracks you see in the rubber were already there before it was de-rusted. As a side note, I noticed no change in rubber hardness by pressing on the bushing by hand and the surface of the rubber actually seemed more natural and supple (not hardened OR softened and spongy). Click image to enlarge.