2004 E320 wagon intermittant starting

[zakkkk]

My wife's wagon recently started acting up.
It intermittantly refuses to start maybe once out of 20 tries. The other 19 starts are perfect half crank engine starts.
On the bad starts there is only that clicking sound. The sound like your battery is dead. So I replace the 5 year old battery.
But the problem still exists.
Is there a common problem on there 211's ?
Like faulty ignition/key switch or transmission switch or something?
Any help would be appreciated
jz