I'm not sure when they started galvanising the 639, I thought it was 2005 (based on build date of course ... not when it was registered). You can tell by the existence (or not) of the 12 year bodywork warranty.
But 2004 ones definitely weren't - a friend has a 54 plate that's in quite a bad way (nearly as bad as a contemporary E Class ).
I'm going to keep mine for a while,just bought it last year.
But the next one will be 2007+ and met. just to play safe.
P.S.Bill,is that original MB flooring in your "beast" ?
I like it a lot.