RE: my 1995 E320. I replaced the wrong coolant (2 years ago) with the correct MB coolant. The expansion tank was gross (I bought this car just 2 years ago) so I replaced that as well as the hoses and the water pump. The system works great. The entire system was drained (including at the block) at that same time. I just had to replace the coolant tank float sensor today which meant draining the tank. I noticed this amber-colored gel clinging to the sides of the expansion tank. It was as slippery as coolant, not sticky. What is that? I've never seen that before in a car with a rebuilt cooling system and the correct coolant. Any ideas?