Ive had this problem with the HZJ75 cranking longer and longer before it would start as winter got colder.
It would start perfectly for the rest of the day ,it was just the start 1st thing in the morning that was taking too long.
I first thought the glow plugs were dead so I took them out and tested them and they turned out ok.
While I had the plugs out ,I spun the engine over to see if there was any fuel in the injector lines.
Normally you will see little plumes of diesel shoot out the glow plug holes but there wasnt any.
After about 15 seconds the fuel began to shoot out so I knew air was my problem.
I wanted to know exactly where the leak was so I replaced hoses clamps and checked the filter seals a little bit at a time in the engine bay.
Then I would start it the next day and after 3 days with no change I was beginning to despair
As luck would have it ,it was the last bit of rubber fuel line and clamps left in the engine bay that was at fault.
It was the bit of hose that goes from the metal fuel line to the fuel pump.
I kind of guessed it was that piece as the clamp and hose that was attached to the pump end slid off with almost no effort.
It now starts on the 1st piston to get compression,which takes 1/2 a second
While I had the plugs out I showed them to the local parts shop. He reckons I still have the original plugs in there.
No one ever uses Denso plugs here as a replacement,they all use Bosch,NGK or HKT
Not bad after 13 years and 240 000 klms