I have a new (to me) '95 E300D with 145K, the last 5K being mine. My car runs a couple "needle widths" above 80C on the gauge normally, and in traffic on a 90F day it might reach 90C with the A/C on. My aux fans cycle properly.

At idle when the car is fully warm the oil pressure is a tad under 2 bar, using 15-40 Shell Rotella, and immediately rises as soon as it goes above idle.

The fact that your car has done 350K miles indicates the longevity of this particular 606. I don't think anyone can predict the future here, however, as you are in to some high miles. I did 300,000 miles on a turbo 4 cylinder Mazda, so almost any engine can do high miles. As others have said, check the records, get a decent PPI done. My car needed shocks/struts, motor mounts, and ball joints, which I elected to have a shop do, and that ran a cool $1000. DIY'ing would have saved about half that. If the price is right, take the plunge, I would say!

Rgds,
Chris W.