Been there done that and it wasn't pretty.

In my (now sold) 91 300TE 4-matic, I experienced a noise similar to the one you describe, although it wasn't correlated with engine temperature. It would tick for a day, and then stop for a day or two. Never would do it consistently enough for me get over to my mechanic when it was ticking.

This car had ~140k miles or so on it at the time, meticulously maintained its entire life, and in fact had been running on Mobil1 for some time.

One day the ticking was back, I drove it to the mechanics and they pronounced it as a sticking lifter. When they went to dig into it, it turns out that the #2 cam lobe was really chewed up. $1200 later I was on my way. Don't remember all the details, but even when all the oil changes have been performed at the correct interval, you can still see failures like this.

I sold the car six months later when the oil consumption increased greatly (presumed valve seal work needed) and when we found good sized chunks of friction material in the tranny pan..... The car also had a tendency to eat sets of tires. A set of Michelin MXV4s would last maybe 20k miles even with regular rotation and proper inflation.

I have the chewed camshaft sitting in my garage as a reminder of the car from hell. It was a dream to drive but insanely expensive to keep on the road. For that kind of money I'd rather be driving a 6.9