Floyedie

I have a 413CDI 2002 Winnebago Leisure Seeker which is built in Australia. It has 180,000km on the clock and goes like a Swiss Watch and has never blown smoke. It recently rolled to a halt and had to have a new fuel pump fitted by the nearest Merc Dealer. I have done 2000km since then and went away for a weekend, filling up with fuel as I left. I noticed that 60ks later if I was at idle, it blew white smoke. The next day it blew smoke at start up and the longer you let it idle the worse the smoke. It blew no smoke at all while driving, but stop at a set of traffic lights and a minute later I could have been James Bond. I took it to the local merc dealer who did a leak down test and discovered No 1 was leaky.(they only had one in stock so replaced that one) I think the tesult was worse. They have put injector cleaner in x2 to see if that fixes it. I have discovered that if I go to neutral at the traffic lights and increase revs to about 2000, and then knock it back into gear to move off, it does not put up the cloud. Also if you just let it sit and idle and then rev it, it has a puff of black followed by white. The Merc guys say replace all the injectors, but what else can cause this ?. Bad Fuel, Electronic Diesel control, or should I just pay the $600 each for the othe 3 injectors ?.
Thanks
Floyedie