My 1989 300SE has the following symptoms:

There is ticking sound on the top of the engine, it is louder toward the distributor cap, to be precise it is under the oil cap.

I opened the oil cap while the engine is running, the ticking is synchronous with the movement of the rocker arm.

When I accelerate the ticking gets louder and faster and faster.

Today I opened the black cover (enclosure) so that I could see the camshaft, rocker arm etc.

The first two (I mean one on the left and the other on the right) rocker arms, this what I observed:
These two rocker arms are not stable or not fixed, for I was able to move them horizontally with my hand. Secondly I held the rocker arm and twisted both left and right it made a click, click sound.

Nine out of the 12 rocker arms have the same symptoms.
The other 3 rocker arms are solidly stable and could not move them.

Here is the picture of the rocker arm.

It’s like the whole in middle of the rocker arm is too big and hence some free play.

Whether the engine is hot or cold the ticking is there.

According to the forums on this website, my conclusion could be that it is the hydraulic lifters. But also in this case I have these rocker arms which are kind of loose, it’s like the bushing is won out.

Please help.