[W126 Coupe] hydraulic leveling fluid level

[Paul Samarin]

I think my fluid level is low.  I assume it's the large canister in the 
very forward right side of the engine compartment which appears to be 
slightly larger than a 1 liter soda bottle.  I don't see any level 
indicator lines on it, but the fluid level is a couple inches below the 
top of it, and the car seems to be riding a bit low.

What is the proper level of fluid?
What kind of fluid to I put in there, and where do I buy it?
I believe Nathan uses ATF for that, but I don't know whether I'd have 
to flush the existing clean before replacing with ATF.  If so, how much 
ATF will I need?  What brand/type?

Thanks in advance!

Paul
86 560 SEC, lowered...now, more than ever