I have a similar problem, almost a miss, but have new plugs, wires, rotor, cap, mixture is OK by duty cycle (I've not checked the EHA yet), so suspect something fuel related like cyclical lean running or some such. Could be at bad fuel distrributor.
All plugs look pretty much the same, slight tan deposit. Milage is fine on the highway (22 or so), stinks in low speed driving.
This kind of shake will fatigue the mounts, I'd bet.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!