You are running too rich, and need to find out why. Can be a bad O2 sensor (surely fouled, too, by now) or a missadjusted mixture, ignition problems, a bad EHA, and so forth. No way to tell without testing.
You can check with a multimeter with a duty cycle setting (Sears has a good one for about $30) -- duty cycle signal is between sockets #2 and #3 on the X11 diagnostic socket on the fender by the coil -- it's the one with a cap screwed down on it. Should read 70%, I think with key on and engine off, going to about 50% with engine hot and moving around a bit. Steady 50% running all the time is a bad O2 sensor, very high or very low is mixture not being controlled.
You also need to check the EHA current, requires a cricuit completing milliammeter that can read plus or minus 20 mA easily. Digital ones are a bit steep, but an old analog will work fine.
If this is over you head, check out the very good DIY article in the DIY section from Steve Brotherton, or take it to a mechanic, you need to get this fixed.
The hard crusty stuff is oil burning ash -- for sure you have leaking seals. Synthetic oils leave less ash, so that may help, and they are also higher viscosity hot. I use 15W-50 Mobil 1, but any full synthetic of similar viscosity will work. I would not use 10W anything in Miami, MUCH too hot in the summer!
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!