I put power steering fluid in mine when the main pressure hose started leaking. Then replaced it with the Febi fluid once I had the problem repaired.

Here's a write-up on how to repair the main pressure hose if that is your problem.

Repairing hydraulic hose for SLS hydropneumatic suspension on TD

Leaky hard lines seem to be the biggest pain in the neck from what I have read on here. Most likely to occur in the rust belt I think.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13