Yes, the latest MB spec coolant is blue. It's a pity it looks green through the reservoir as the reservoir yellows with age. Honda brand coolant is a darker shade of blue and there's a following of MB'ers who swear by it.

A 722.3 should be good for 250-300K miles with basic service. With the symptoms you describe, it doesn't make a lot of sense to drop it for new seals alone, though consider seals that can be replaced without dropping the tranny if you don't plan to put a lot of miles on the car.

Sixto
87 300D