Toyota Prado: Engine rattle

I purchased a new Toyota Prado 3.0L GXL common-rail turbo-diesel in 2006. In 2007, while towing a 1750 kg caravan up a small incline the motor lost power for approximately 30 seconds. After travelling for only a few minutes the following day the motor began to rattle. I pulled over and turned the engine off for five minutes, and when I restarted it the rattling was gone. After driving another 100 km to the next big town we asked the local Toyota dealer to take a look at it, but they found nothing wrong. Again, when it had the 20,000 km service I asked the dealer to check it, and again they found nothing wrong. At the 30,000 km service in 2007 I spoke directly with the service manager about the previous problems and also mentioned that the motor would rattle when it was started from cold. It was checked and everything was said to be fine. I mentioned the above problems at the various services through 2009 an d 2010 and once again they could find nothing. I even left it overnight so they could start it first thing in the morning. Although they could hear the rattle they thought that it was normal. In mid-October this year when my wife started the car it backfired and black coloured smoke came from the tail pipe. The dealer assured me that it was fine to drive but I should take it to them the next morning, which I did. When I arrived they put the computer on the car and found that all the readings wer e fine, but the service manager suggested I bring the car back and have the sump taken off and the oil pipe checked and cleaned out of any sludge. When they did they found that the number one fuel-injector was leaking and that the car needed four new injectors fitted. They contacted Toyota to enquire if this work could be done under warranty as the problem had been known since 2007, but it was declined. The cost of the work was $3336.25 and two weeks without a car, one week for Toyota to decline the service manager's enquiry and one week to have the work done. For the first time since 2007 the engine doesn't rattle. Is this just a coincidence?