Mike
Here is a great thread by Goose on changing the coolant,
http://www.venturerider.org/forum/showthread.php?t=37353
I always use the pre mix Honda stuff from he dealer, not cheap but I know it is the correct stuff.
Avoid any auto coolant that has silica in it, they add silica to act asa scubbing agent to remove corison build up, but it can be harmfull to the water pumps on the bikes, I see this on both Yamaha forums and now Goldwing forums I frequent.
I have been known to let mine go well past the recommended time and interval, with no issues.
Funny I just did the coolan change on my Goldwing last week end , because it had hi the recommended miles, and not really having any history on the bike, I thought it best to know where i was with it.