The broken part is known as an "oil connector". There are several designs, depending on the year of manufacture. Yours is the latest design, which supplies full oil pressure to the rocker shafts. New parts of the rocker arm system are very scarce, unless you happen to find "new old stock" parts somewhere like Ebay. Fortunately, there's a pretty good supply of serviceable used items. Those rocker shafts are definitely too deeply grooved to be cleaned up and reused. I see new ones on Ebay pretty regularly. Some machine shops can bore out the rockers and install bushings, which makes them better than new. If I can get over my current bout with Covid sometime soon, I'm considering getting tooled up to recondition rockers in my shop.
Jerry
