I put new mounts in about four or five weeks ago -- helped quite a bit, but it still rumbles.
The only thing I can find is that #3 plug is a little darker than the rest, donno why except maybe a dribbly injector. This could make the O2 sensor think "rich" and lean out accordingly, so that it's actually running too lean with excess fuel dripping from #3. I suppose I will have to spring for new injectors soon, if I cannot find anything wrong with the fuel distributor.
I did replace all the vac lines, including the idle control valve hoses, something you might want to look into -- in my case, I think the idle mixture was set with all the leaks (I replace ALL the rubber connectors, every single one was shot!), so it ran very rich afterwards. Still thumped -- sure hope it's not the fuel distributor.....
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!