Painting - stain/seal and prep for ext. redwood

i have a redwood sided house that has been stained with a few different kinds of polyurithane (sp) and stain with minimal luck. the stains usually look beautiful but peal after a year or two of sun and weather. unwanted mildew has formed all along parts of the siding, but i want to maintain the rest of the weathered color. is there a stain of some kind that will hold up to the weather? is there some kind of bleach mixture that can wipe out the mildew yet not significantly change the weathered appearence. also, i am curious as to the best preparation methods, over the last couple of times i have simple scraped off the pealing polyurithane. i will try sanding it, but i am curious if the proper pressure powerwash might prep it properly yet leave the weathered appearence?
many thanks
thebigchill

http://forum.doityourself.com/showthread.php?threadid=79690&highlight=redwood+siding