If it takes time to start the engine, there is fuel build up and this will manifest in a small amount of "exhaust crud". Operating the glow plugs twice warms the engine more,thats fine but it points to a minor problem somewhere. Probably the glow plugs failing, or are you in an area of exceptionally low temperatures?
Was looking at Grand Voyagers earlier on ebay. Done it price low to high and there were about 10 different ones being broken for spares. Might be worth a few emails.