Diesel Injector Pump Leak
 

I have a 1983 B2200 diesel. There is a large square nut with a smaller 12mm hex bolt in the middle of it in the middle of the delivery pipes on the back end of the rotary injector pump that is dripping diesel at a fairly steady rate. Is this something that might be fixed or does it mean a complete (and expensive) general overhaul of a worn out injector pump. I don't want to just go tightening anything, particularly when I don't know what these nuts and bolts do. Any help would be greatly appreciated.

Thanks

Russell