Actually, on the 124 cars the self leveling pump is not on the engine block, as it was on the 123 wagons. The 124 uses a so-called 'tandem' power steering pump. It's really two, two pumps in one - one for p/s, a separate pump for leveling. The reservoir for p/s fluid is integral, the reservoir for leveling fluid is remote. The pump is on the intake side of the engine, far from the exhaust system. So I'd guess it doesn't really get all that hot.
FWIW, it's been about 2.5 years since I flushed/changed my system and the fluid still looks like new. I'd bet any blackness is minute particles of degraded rubber from the accumulators. (All the lines are solid, right?)
I didn't realize Fastlane also sold the fluid, otherwise I'd have included them in my plug. Certainly not trying to direct business away from the sponsor of our site!