noisy hydraulic lifters in M104 hot and cold...Help!

[Garmar70!]

Hi all, my first post.
I have just bought a 1991/92 W140 300SE.
Fitted with the M104 engine.
My problem is the hydraulic lifters. Very Noisy from cold and hot.

I took the rocker cover off a warm engine.
All of the lifters were not pumped up.

So by my logic whatever feed the lifters is blocked.
I have no idea where the oil passageways are, where to look.
And how to fix this without pulling the engine out and stripping down.
(it wasn't my intention to have a major overhaul straight off).

So how are the lifters fed oil?
Has anyone else had this problem, and what was the resolution.

Any advice from M104 gurus would be most welcome.