I block the tubes off toatly,the oil will returnfront and back with out the tubesas main drains in both ends of the valley.my 292 ranchero has lots of miles and presure is 25psi at 600rpm hot, 60 psi at 2500 hot. most of todays oils moble 1 10/30 quaker state 10/30 bothe have plenty of moley and aditeve package to be a vastley beter fit for flat tapet cams.rotela t is not good for ftapet cams,and is for diesel engines.I have dismant maney y block rocker shafts,most have badley scored shafts and rocker arms,all do to poor oiling,90% have most damage on the end that has bleed tubes.fe fords have no bleed tubes and full presure to rocker shafts. very few rocker isues ,no cam isues.i am convinced most yblock cam isues ar a result of poor lube to rockers,rockers scoring the shaft place heavey load on cam lobes, poor oil to push rods inhibet lifter rotation which wear cam lobes. just my take on rocker lube.