I don know what kind of shape your E420 is in, but unless it is costing you a lot of money or sanity to keep it, you'll probably regret getting rid of it. As much as I like my E430, I still regret trading in the 95 E420 I had three years ago.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired