Hey guys I've noticed a loud tick that has become increasingly consistent over the past few weeks. It occurs whether the engine is hot or cold and proportionally increases with the engines RPM. I'm beginning to think the noise is from a sticky lifter as opposed to a fuel knock on an injector. I was hoping someone with a better trained ear could tell me.

Some background info on the car:
1987 300d om603 turbo 118,xxx
2nd owner (owned for about 6 months)
service records indicate fuel injectors are original
glow plugs replaced in 1999 roughly 20k miles ago (it wasn't driven much the last decade)

Here is the link to the video of my engine ticking: 1987 W124 300d Lifter Tick - YouTube

NOTE: the engine is currently at operating temperature

Any thoughts or opinions are greatly appreciated!