TD5 Defender wont start

I have this defender since 2004 and have fixed a lot things on it over the years but I'm sure what the problem is this time ?
I replaced the fuel pump about two years ago and the injector seals around the same time, so I'm hoping that they are not the problem this time .
It was getting hard to start before Christmas but I replaced the contacts in the starter motor and all was good for a week or two. After Christmas it took a long time to start maybe 30 seconds spinning before it fired, this happened a few times and it let me down eventually
It started a few times since, when I sprayed paraffin into air intake but that wont work anymore (it tries to fire when paraffin reaches the cylinder's but wont)
Oil wicking its way into the ECU is a common problem on the TD5 but mine is fine and its half full of diesel .
So any suggestion on where to start looking for the fault?
Thanks for any help.

When you turn the ignition on, does the temp gauge go into the red (even when stone cold) and does the glow plug light not illuminate? If yes then check the cleanliness and tightness of the relays under the drivers seat, near the ECU. Also check the earth near the ECU too.

I wasn't sure Wireman so I just went out to check and it's all normal on the dash.
Thanks for the reply.

slim jim said:

I wasn't sure Wireman so I just went out to check and it's all normal on the dash.
Thanks for the reply.

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You’re starter motor might be dodgey, sometimes they turn over fine but disturb the crank sensor reading, which in turn fails to start, check you’re fuel pressure reg isn’t leaking

Ps avoid the paraffin treat in the intake, that wont fix it, but make it a lot worse