When I was adjusting the valves on my 235 engine in my 55 1st series I noticed that very little oil was coming out of the rocker arms for 4,5 and 6 cylinders where as 1 through 3 had a lot of oil. There appeared to be a small hole in the bottom of the small tube that supplies oil to the rocker arm . I plugged the hole but that did not change the oil problem to the last three cylinders. Is that hole there for a reason? the engine was rebuilt about 15,000 miles ago and has run good . I was thinking maybe it is time to rebuild the rocker arms . Does anyone provide that service THANK for any help.