How do lash adjusters work?
Moreover, how do you know if your lash adjuster is bad?
The ford manual says that a properly functioning lash adjuster should bleed down in the 5-25 second range. So, if you can depress it with your fingers and it springs right back, it's bad. If it takes longer then 25 seconds to bleed down or less then 5 seconds, it's bad.
In this way, how much does it cost to fix a lifter?
Depending on where you buy, component costs can vary. Just the lifter component will cost anywhere between $4-$40, the intake manifold gasket which you will replace is another $8 to $50. I am taking into account you won't need to replace the camshaft or Camshaft Bearing, Pushrod, Pushrod Cover Gasket or the Rocker Arm.
Seafoam CAN be used in the oil. However, it's not going to fix a lifter tick. If you're running a ticking lifter when it's warmed up, it's quite possible that it's bleeding down and not holding as the oil flows quicker once it warms up.