Firstly get hold of some fresh viton or even rubber O rings and redo all the plastic pipes on the pump/filter. - Be sure to remove the prefilter strainer and replace its O ring too. Clean the strainer while its removed.

Also buy a bulb type diesel fuel primer pump - pump it up, you can also subsitute this with an electric fuel pump. This makes sure our pump is getting all the fuel it wants.

I would also try a part gasoline part MMO mix in the pump to free up any globs of grease that build up and cause the pump to stop working. (saw a similar case very recently - the amount of greasy slime was incredibly bad).

Hope your engine has compression, rings can stick hard in their grooves with such fuel being burnt in the combustion chamber.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)