So i had that tick for a while now that would come and go even with new lifters after the h/c swap...... Pulled off the oil pump and 1/4 of the o-ring is missing ....SHOULD I WORRY?

 

The "O" ring needs to be there, it was probably cut during install of the pick up tube. If it were mine I probably wouldn't loose too much sleep.

 

The question is where is the missing piece. How many times have you changed the oil? If you haven't, you may be able to cut open the filter and find the piece. I would also blow out the oil gallery between the pump and the filter with the filter off the car to ensure there are not parts in there either. Careful with the new installation. I used Redline Asssembly Lube when I put mine together, helps the o-ring slip right in. Just in case, make sure the o-ring is on the pickup tube during assembly and leave the oil pump bolts out until the o-ring is seated which allows the oil pump to be rotated while assembling.