Carb cleaner, brake parts cleaner, or propane from an unlit propane torch all work. Too much carb cleaner can damage the O2 sensor, so don't overdo it!
The only thing wrong with the plugs you took out was worn side electrodes from the milage, the centers look OK -- the great advantage of Platinum plugs. Mine were black and ashy, but it was running very rich (I fixed a bunch of vac leaks, the mixture appears to have been set with them leaking).
The last time I looked for Bosch Coppers for the 300TE I had to special order them, put in the +4s instead, and bought Champions for testing -- they worked fine this weekend on a 1000 mile trip, but will change them back when I get a chance.
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!