Dexcool is okay in GM, but don't believe the 100k mileage claims. I drain/flush every other year.
Xerex G05 or the OE MB stuff. Light yellow color, like when you have one too many beers after a night.
M103 is super easy to flush. Block drain is around the No 5 cylinder exhaust port. Check all your hoses, there's quite a few behind the main firewall. Good simple maintenance to keep you on the road and not stuck somewhere.
Verify your coolant temp senders are good in the head, usually the aux fan one is bad. Also, the M103 seems to run slightly higher coolant temps than a Diesel or V8, probably due to the smaller radiator which made no sense to me either.
Anyway, I have a new cooling system in mine and I see 82-97°C depending on the season, nothing higher than that while operating. I also dropped to the 79°C thermo from the 87°C and didn't notice much aside from the fan clutch not coming on all the damned time in the summer...
I have driven the car a few times since it cooled off and in the low 40°F temps the motor got up to 80°C+ easily, so the thermo is fine. Also my Turbo BMWs use the 79°C from the factory.
Probably more than you wanted to know.
