I have a 62 1/2 ton Chevy truck with the 235 engine that had the same peoblem you described. The only solution I have found is to replace the lifters with solid ones and adjust them as solids. The engine is a little more noisy but no more leaking down. I did the same thing to an earlier 235 and ran it for many years and over 100,000 miles with no problems! Some readers will tell you you can't run solid lifters on hydralic cams but you can...
