Some people forget to do while rebuilding them...
8. Once all your parts are cleaned start putting them back together, first the spring into the lifter body, then the check valve.
9. Hold the lifter upside down and push on the check valve 5-10 times to get any remaining diesel fuel or carb cleaner out of it.
10. Submerge the lifter in NEW OIL so that you can push the check valve open and closed from directly above (right side up). Push on the check valve 5-10 times to remove all the air and to be sure it is full of oil. Remove the lifter from the oil, but keep it over the container so you don't spill oil everywhere. Place the plunger into the lifter body and make sure you cannot push the plunger down by hand, if the plunger moves then repeat the process (If you can still move the pluger after a few re-tries then your check valve assembly is shot and will need to be replaced). Replace the little metal cover. In order to get the cover to snap into place you will need to compress the lifter 1mm or so. This will allow you the needed clearance to easily snap the cover into place. I used a very large C-clamp.
11. Reassemble in reverse order, REMEMBER to KEEP ALL ROCKERS TO THERE RESPECTIV POSITION AS WHEN YOU REMOVED THEM.
Well there you go you are now done and can enjoy once again a very quiet motor =)