Seized CAV rotary pump rebuild | Ford 3000 engine rebuild | Part 2 

Not really sure, sorry mate. Because the DPA pump is lubricated by the flow of diesel through the elements, it increases the amount of varnish you will find in the pump. This is why I do not particularly like them, compared to a Simms Minimec for example which is lubricated by its own oil. The only thing I could think is fuel stabiliser in the tank, as varnish usually only develops from the residue of old fuel that has been sitting.