RE: GO questions
I think that I might be able to offer some input on some of your questions, but let's see.
Regarding the use of a weedfin or regular fin, I would select a regular fin, unless weeds are a problem at your local site. A more vertical oriented fin will give you more power, especially if you want to have a windward ability.
In my opinion, footstrap position starts at the rear most positions, and gravitates to more forward posiitions if you feel the need to be more settled. I start with a more aggressive position because it usually represents a more speedy focus. If more control is needed. inboard or more varied positions can be an alternative, especially for some varied sized sailors.
I'm thinking that the mast position for a 9.8 is going to be in the middle to the forward section of the mast track, but I'm projecting at bit because of my inexperience with the GO 170. However, I would start at a point that is more aggressive (more rear in the track) to find the best balance with the sail. Also, how you have rigged the sail says a lot about what you need to do to feel optimum.
I'm not sure about your last question. I've heard about ways to resolve the yellowing, but I can't remember the details at the moment. I hate when that happens, but what can I say. A senior moment. Maybe Roger can offer some valuable input here, since he maintains a healthly stable of gear for hard use.