Relyon

The heads where removed and cleaned and gone through and new lifters installed and this solved the ticking problem for about 3000 miles and the ticking started again and the oil pump had to be replace because of lost pressure, that worked for about 1400 miles and the ticking started again, so pulled the valve covers use a stethoscope and found the ticking coming the intake at cylinder #2, so I pulled the pushrod and it had a place close to the lifter on the side where it had been rubbing and also a small nick on the tip at the lifter.
What would cuase this and what would be the fix for it?