Stuck Compensator/Lifter

[AZIRRIGATION]

Vehicle is a 1987 560 SEL with 169000 miles. New timing chain, timing chain tensioner, and top three guide rails at 167000 miles (6 months ago).

I decided to check the hydraulic valve clearance compensating elements (05-211) since I had cam/valve covers off. While checking each compenstor I was able to push down the compensator for the exhaust valve at cylinder #4 and now it is stuck down and the rocker arm is loose. The manual say's to replace any compensator that can be pushed down faster then the others.

Could this be causing the loud KNOCKING noise?

How do I get compensator unstuck? Can I turn engine over with the rocker arm being so loose?

Is the "hydraulic valve clearance compensating element" the same or another name for the "Cam Follower", "Hydraulic Lifter", or "Hydraulic Ball Stud Assembly"?