Not so sure what an ES 420 is, as that's not a Mercedes term.

If it were E420S that would be a V8 station wagon, not sold in USA.

Instructions are in owners manual, but surely it's easy to find the clips at the bottom front of the seat. Just lift up.

That's for a sedan of course.

If it's a wagon reach between seat bottom and back and rotate bottom forward.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles