TRW is very good and are the OEM manufacturer for many of those parts. When you buy a TRW part you get the Porsche part with the little triangle that designates Porsche ground off. Meyle is very good as well.
- For #8, you can get TRW, either the 986 (JTC1186) or the 987 (JTC1316) part for around $100 each from Amazon.
- For #9, Meyle, I just got 2 of them for under $200 from FCPEuro, I think the price may have gone up very slightly since then.
- For #17, I have aftermarket rennline links, but either TRW or Meyle (!$77) would be good.
If #8 is bad you probably are hearing some knocking and certain noise coming from the back, seer this thread for more details:
rear suspension noise over tar strips
If it was me (and it is since I am actually replacing all these components front and rear right now as part of a wheel bearing and new suspension project I am about 3/4 of the way through) I would do them. Then you will have all new joints and bushings, etc...
Edit: note that I am not endorsing any vendor, your results may vary, etc... Pelican is very good about having things in stock instead of having to wait extra days so for speedy results they are often the best choice.