Wolf oil burner

[Donza]

Hi all. My central heating/hot water is a wolf oil burner. Been in the house since it was built (70s).
My problem is the noise coming from this valve on the main heating pipe from the boiler. It kinda tinkles and rattles which then travels through the pipes making the radiators all noisy.
I’d replace it but can’t source a new one. ( I’m in Germany btw)
To be honest I don’t even know what it is, it has a one way thingy inside and a sticker saying auto / on , on the side. There’s also another on the return to the boiler too.
Any clues/ helpful hints?

 

[oilhead]

Try opening and closing it a few times. You may also be able to tighten the spindle up with the hexagon screw at the back.

 

[Donza]

Cheers, I tried that already. I took of the cover at the back, it just opens into the shut off / turned on side of the valve.