How much of the XL-18 do you add? The whole bottle?
Yes... the whole bottle is added. It is a small bottle of less than one ounce. Super easy to do and IMO, worth the cost.
I'm not sure on the bushing but I know several folks have stated that aftermarket bushing kits do make a difference. Please report back on the bushings (may be a good experiment to do the bushings first and report the results, and then add the xl-18). Good luck!