OM603 loud ticking when cold?

[83w126]

I have put about 6500 miles on the car since I bought it, and this problem has been getting slowly worse. Sometimes but not always, when its been sitting for a couple hours or more, it will make a loud ticking sound that sounds like an exhaust leak when i first start it, then it slowly gets quieter then stops after driving for a while. Sometimes it doesn't do it at all, and its always very quiet when its warm. I have changed the vaccum pump and serpentine belt tensioner, and other than slightly leaking from the stop lever seal I don't see any fuel leaks. Any ideas what might be going on? I haven't checked the timing chain stretch yet but I am going to do that as soon as the valve cover gasket I ordered from the dealer shows up.

[pawoSD]

Ticking when cold is worn hydraulic valve lifters. Solution is to replace them. Had to do it on my OM601 and it was completely quiet afterwards. They leak down their oil pressure when the engine sits/gets cold, then have to pump back up again when the engine is restarted. The time they take to re-pressurize is when they are ticking.

[86-300sdl]

Ditto