I concur.. recently lifted up the stripping on the passenger side of my R53 and noticed some rust eating away the metal just under the stripping. Is this cause for concern? Rust is like a cancer on cars, is this correct? How to stop it from spreading and eating away my chassis?

 

Sadly tragic fact dammit friggin' MINI!

Pretty huge thread on the topic of sill rust:

https://www.northamericanmotoring.co...ispreloading=1

I am a victim too and would love to hear of any resolution to fix the problem, but so far I haven't even read definitively about the design flaw which creates the problem in the first place, so even if you correctly repair a rusted/rusting sill with virgin metal, the same problem may most likely re-occur.

It is a major bummer.