I don´t know if there was an Coilover built für an TDS,
but look @ Supersport, KW, FK, or Reuter Motorsport.
Supersport and FK are the cheapest way for Coilovers.
KW is much more to spend on, but it´s worth every cent.
Have yoo already asked google for " 525tds Gewindefahrwerk " ?
Maybee there are some to find.