I'm a bit concerned about my '83 240D, it's developed a clicking/ticking noise in the last few weeks.

I can't/can only just barely hear it while idling or maintaining a constant speed below ~45 mph. Above that, or while accelerating, it gets louder when given more throttle.

I've had my drive shaft flex discs replaced recently so I know it's not that (I searched before I posted this question) but have seen mention of things like, vacuum pump, oil pump, timing chain, etc.

I can't generally hear it when the car is parked/stopped, even when I rev, so I'm not sure really how to begin diagnosing. Any pointers?

EDIT:

I went downstairs and checked the oil. I added a quart and a half less than a week ago. There wasn't even a spec of oil on the dipstick. I added almost 3 quarts, and it's now in the middle of the "okay" range. It's never consumed oil like this before -- in the interval between when I bought it and when I did the first oil change, I had to add maybe 1 quart total.

There are no oil spots/drips under the car at all.

Only thing I've done differently is, I didn't add Power Service to my last tank. So, basically, nothing different at all. I'm very worried, now.

Does anyone know where I can order those clone 616 engines that have more HP than the originals do? If its something serious, I'd rather do that. I think they're Tempo?

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER