>>>2. Wait for the solid glow plug light to go off

>>>3. Turn key back, and turn all the way over to crank.

Am wondering why you turn the key back before cranking the engine??

What you are doing might interupt the electric circuit that glows your plugs..... or initiate another glow sequence that goes unfinished, as you turn the key directly into starter mode.

On my 112k low mileage '79 240D, i glow the plugs until the light goes out then turn the key *directly* into cranking mode. It has never failed to quickly start..... even with the older loop-style glow plugs.