lost all power other day pulled up and discovered under bonnet everything covered in diesel

the bosch pump at its lowest point has a plate held on by two bolts, one bolt had dissapeared , i assume rattled out, and the other bolt was bent by some kind of piston behind plate striking plate , this where all the diesel was spewing out of , am i right in assuming this plate covers the actual diesel pump itself ? there was a o ring attached to plate which had split, and to get me home i sourced a similar size o ring and bolt, bit of cranking and it went , phew !
a pump on a friends transit similar year has four bolts over the pump ?
well it went again today, i think the rubber o seal i put in before was nipped in housing, my fault, but it was cold damp and miserable at first attempt and 30 mile from home
does anyone know what is behind this plate please ? and any help
heres a pic but not quite clear from a phone camera thanks ...
