pump appears to be seized solid

Despite my efforts, the pump seems to be, in a technical term, knackered.

The rack won't move more than a 1/16"

I pulled the drain plug and a very dieselly mix came out... felt like a light oil, rather then the engine oil that is supposed to be in there.

I have put new oil in, liberally soaked the internals in releasing oil, yet nothing.

I did plan on pulling the top of each of the cylinders. There is a knurled nut that can be undone beneath each fuel union... but they are too tight to undo in situ. Its a shame, as I might then have been able to remove the check valves and tap each cylinder to free it up.

Here's the offending article

You can see the knurled nuts quite clearly in this picture. I may have another go at them in an hour when the penetrating oil has done its work a bit more.