Here's a general question: How do you identify, in advance, what parts will be necessary for a repair (including all the various fasteners, o-rings, etc), and order them? Certainly for simple repairs, any consumer auto parts store / website will be able to provide. But for more specialized parts, what do you do? Or, what professional resources (distributers, catalogs, guides, etc) are available to the DIYer?
The best resource that I have ever used is the service manual for my vehicles. They are available at most auto parts stores. Those manuals have the "exploded" view of parts that can be rebuilt and have all the instructions that the mechanics at the dealership use. Those will list what parts you need for a particular job. Also I usually Google for something I am going to do if I have never done it before and I either find the manufacturer manual also or someone has a write up or video about how they did it and what they needed. Forums for that vehicle can be a big help also as most people on forums are DIYers.
I usually have a look at youtube. There is probably a video of a guy doing exactly what you are planning to do and he will show you what you need and how to do it.
Also, get your hands on a Haynes manual for your car (if available).
If that doesn't work, as a question on a forum dedicated to your specific car brand, e.g. http://astraownersclub.com/