My reason for doubting any drag is I have a motorhome that I've had some brake problems in the past (big problem, but that's another story for another forum ). Now the MB isn't a motorhome I understand but from my experience a dragging brake that is a problem is going to be several hundred degrees F (350, 400 maybe even higher), not just the slightly elevated temps you metioned. Also when i had my issue, i became very astute to my temps on all my vehicles and it isn't uncommon for them to be well into the range you mentioned or even up to 200 and a bit above if you have done some repeated or heavy braking before checking. Just my thoughts and probably only worth what you paid for them!

Regarding the wheel bearings, if they haven't been packed recently that is an easy job and worth doing anyway. I would not replace them, no reason for that unless you get in there and find some obvious worn bearings. You will need new inner seals but those are only a few bucks each. I recently packed the fronts on both of my W124's since they needed adjusting (tightening) anyway. It may not be the problem, but its a good routine maintenance task that probably is seldom done but an real easy job and worth a couple hours. Sounds like after that you will have eliminated all the potential problems with the front wheel making the noise. Good luck, these things are fun to do anyway.

Any chance it isn't coming from the wheel and it's an idler bearing or something? I am not familiar with the 87 260E but I know on the mid 90's gassers (E320) the smog pump pulley and tensioner pulley (idler) can wear out. I assume your car has some of that kind of thing that could cause the noise, maybe only when revving it up when driving? Again more free advice that is probably worthless.