1998 Other Holden Models Car turns over but won't fire

Hi,
We have a older Holden Rodeo, 3.2L V6 with approx. 260 000klms on the clock. Been running fine and was due for a service, partner filled the tank from empty with dirty fuel, black particles, and an not so clear looking fuel. Car drove 30klms fine, then spluttered and died. Logic said the fuel was the problem, so 2 weeks later and countless $$$$ the mechanic tells me he drained the system, injectors were cleaned, replace filters etc, had an auto electrician go over the car, checked the timing belt because one side is 175 compression, other is 100 so thought that might be a problem, that was fine, gone over the motor pretty much completely, its getting fuel but just will not fire, turns over with lots of effort just not going the extra stage. Mechanic has now pulled the rocker cover (prob not right term, still stuck with the old motors) off to check the camshaft etc and said that was all fine but said there was a fair bit of sludge in the motor, and we need a new motor or new car. Any ideas, neither of the mechanics options sound terribly exciting to us, as the car ran perfectly until this tank of fuel.