Blue58,
What year is your 235? Chevrolet used different methods for getting the oil to the rocker arms. The 1953-1958 (or 1957? I forget) used a tube from near the #6 tappets to the upper center of the block. The later engines did not use the tube. Some later engines were fitted with an an external tube when the internal passage gets blocked. The tube and fitting with the earlier blocks can also get blocked, as John mentioned. Here is one many posts that address this problem.
235 oil questions . Here is
another post . Search this BB for other discussions.
Getting the oil to the rockers has always been an interesting adventure with these engines. My first experience goes back to 1955, when I amazed my father (and myself) by solving a noisy rocker arm problem with his 1947 216; the tube that should stick into the hole in the head to route oil to the rocker arm shaft had slipped out. I put it back in and the 216 ran well for another two years.
