Molybdenum deficiency would be my first guess. Mo is partially mobile and it's getting localized to the seeds, causing older leaves to have irregular chlorosis. If so, the new leaves will get smaller and paler and new pods having less seed filling progressively. Plant might be less resistant to various stresses as well. If the bed received lots of high N fertilizer, it can make soil acidic and reduce molybdenum availability. If your buddy wants to give it a try, he could gather >10x biomass of clover or other legumes, dry and burn to get the ashes. Drench soil around the bean with the ash water with a couple pills of vitamin B12 for cobalt.