On a disco it is a very common fault due to a pipe being too short and the pump fractures as a result of be pulled on by the short pipe. this is fixed by fitting a new pump and a modified pipe that has a "pigs tail" in it.
On a Defender this does not happen due to the filter being in a different place.
The pump is a sealed unit and cannot be overhauled.
Land Rover often go short of these lift pumps, so much so that I keep a shelf full of pattern parts to supply the main agents when they cannot get any.
Before you condemn the pump check all the pipes above it especially the fuel return rail from the injectors. These often chafe on the rubber rocker cover cover. It could be that a pipe has just worked loose.
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