Do you still have the fuel receipt.

That's what I put in mine without any problem...
I did have to do the master innards and a replacement slave cylinder.

Did they replace the water pump. They leak out of the (telltale hole) when hot then seal when cooling down. Get a dentist mirror and torch and check the pump housing for signs of a leak

Open the back door, remove the grommet at the van side, it's inside the pipe a few inches inside the rear roof. Squash the pipe gently with your fingers, you will feel it, it's in there for holding the screen wash near to the nozzle so it doesn't run back to the bottle

If you pull out the pipe gently on the van side you will find inside a little one way valve this also gets blocked. Trust me, it's in there.!!.

They screw out and can be replaced

I went to the opticians to get a standard test when I was starting to notice the brighter modern lights were hurting my eyes, I was surprised to find I needed both eyes cataract removing, having had that done, I find the brighter lights are still as bad, but an awful lot clearer lol.

On the bottom steel hose that is under the driverside foot plate, just In front of the pedals is a nipple with a rubber cover on it. This is how they may have filled from bellow in the factory as it's the lowest point. It's on the drawings but not described....

The pulley is a rubber bonded multi piece job. It is coming apart. It's hitting the front of the engine so don't run it .....

Check the operation and voltage of the glow plugs, could be low voltage from battery, then check voltage to the rail. Is it damaged or shorting. If all tests well you could remove/replace glow plugs. Starter motor contacts failing is another maybe, they are known to fail inside the starter itself ...

I used paddy hopkirk heavy duty commercial, plenty of room above the roof and the bars are long enough for the wide bongo roof.
Google search em.

That's one of the 2 valves which are at the end of that pipe. It's clipped on to the chassis, just pull it. Then remove it from the end of the pipe. Just inside the pipe end is a little thimble one way valve too. Clean em both out.

In my distant bad memory, don't I remember there is a way to reset em. It's either use the buttons to take em fully forward them back, this centralises the auto adjust.
Or maybe just manually push them forward then back.
It makes a horrible noise.
Or is my memory playing tricks.

The fuel tank pick up pipe has a little thimble filter on the end inside the tank, this could be blocked or restricted a little. Take off the pipe that goes into the fuel pump and blow back to the tank, when clear try sucking back towards the pump to help it prime.
The tank itself also has a ...

The inside of the arches originally had spot welds all around the underside of the arch, every 6 inch or so.

Have a go with the magnet, it may show you how little there is or other.