Here's my $.02 worth.

I have used Rust Mort from SEM Paints. Supposedly converts the rust by some chemical process.

Here's a link I just found to some rust chemicals.

http://www.tcpglobal.com/autobodydepot/rustremove.aspx

Bert-NH

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1979 300SD 83k miles Astro Silver Metallic/Black leather #3447
1990 350SDL 202k miles (3L engine from an 87 300D)Black/Grey leather
2006 Pleasure-Way Class B MoHo (Sprinter chassis) 134k miles
2005 E320CDI 270k (car is sooo fast - I can't believe it's a diesel!!!)