Q: What are roller rockers for and what would cause them to have rust

Roller rockers are used to push down the valve spring with less resistance than a traditional rocker. The entire valve train should be constantly bathed in oil when the engine is running and the rollers could only get rust on them, if they were sitting for a while without the engine running and moisture in the engine oil will evaporate to the valve covers and the rockers. Depending on if the engine has been sitting for a couple months or years will say how much rust built up on the parts when the engine was not running. I would not think the rust is anything more that minor surface rust. If you want to get the car looked at before making a purchase, a certified technician from YourMechanic can come to the car’s location to perform a pre-purchase inspection so that you can have full disclosure on the existing condition of the car you’re buying.