For the replacement of parts of the suspension, yes, the fiches will help with that (you need a fiche reader as well, I believe these can be found at used office equipment places or are available new, just enter "fiche reader" in your web browser).
You'll need the fiches for 140 chassis steel spring suspension or hydropneumatic suspension.
Heated seats would best be tested with a DM (diagnostic manual), it would be in the B&A section (Body and Accesories), I am unsure which exact B&A volume it would require. It could possibly be diagnosed by a skilled tech with just the ETM.
On th e power steering, other than leaking at either the steering gear box or pump reservoir, or possibly the pump itself, it rarely bothers. What is the power steering problem? Any actual replacement job would be in the steering microfiche, but I don't believe there is a great source for a diagnostic approach. Let us know what it's doing and maybe we can help.