I'm pretty sure the next Rust is Rust 8, and the connection is Willi Martini, but I'm not sure which Hint is the connecting one.
Rust 8 is the 1952 wreck of Paul Pietsch at Avus in the Veritas Avus streamliner. The Veritas was built by Ernst Loof at Nürburgring, and Willi Martini was employed by Loof at the time. Later Martini built cars at Nürburgring, and, although I am not sure, I think that he might have been working in the same building where the Veritas had been built.
Hint 21 says: This car was built in the same building as the next one, but by a different company.
So I'll try: Hint 21 - Rust 8.