Y-blocks are noted for poor oiling to the rockers and valves. There used to be kits to fix the problem, but you can just Tee into the oil system at the pressure sender and run 1/8" lines under the valve covers to the U-bent pipe on each rocker shaft. It's caused by misaligned or wrong cam bearings not allowing oil to flow past them to passages in the block, up past a head bolt on each side, and to the rockers. A full teardown is required to fix it "right".