PF70 sunblock.

I'm not serious, of course. There is no wipe/spray/brush on magic finish restorer. Short of paint, there are no exterior finishes that last more than a couple years without renewing. Stains/dyes on/in wood also do not survive the sun well.

Only way I know to restore the look is to contact the manufacturer, get the stain/dye recipe(most probably a mix of at least three stains) and the finish variety, strip the finish, restain/dye the wood and apply new finish.

I know that is not what you wanted to hear, it is just the only sure way to get the wood back to better looking.

You could try things like gel stain(modified paint), but that would just do the same thing. And it would be extremely difficult to get a gel stain recipe to match the color now.

Long term, paint is the finish that lasts the longest and requires the least maintenance.

I second the suggestion -- clear finishes do not do well with constant sun and/or water exposure. At least if you are not willing to do regular (annual) maintenance.

Get some good paint and be done with it.