Oxalic acid will clean as well as get rid of nail streaks,(Wolman, cedar deck and fence Cleaner/Britener)
As for the glossy finish,if the finish is really 8 years old, a mild solution of sodium hydroxide(wolman deck strip cut 4:1 or 5:1 even test to see!)will probably do it, followed by oxalic acid to neutralize(just spray a mild solution on the stripped area and wait 15 minute then rinse off) because the stripper will turn the cedar very dark.You can get oxalic acid at a chemical supplier(not recommended if you are unsure of what you are doing) or go to a paint store that sells wolman products and get the cedar cleaner and britener.Or you can get a jug of Zep deck cleaner($6) at home depot,that is also oxalic acid.
So you are looking for:
Oxalic acid.
sodium hydroxide.
Start with a weak solution and add as needed,cedar will get damaged very easily and you will get what they call ,"fuzzies" which are little hairs that appear white and can be unsightly.
For the nail streaks you should mix a slightly stronger solution of oxalic acid in a pump up sprayer and "spot spray the streaks,you will see the rust turn green and then dissolve,when you rinse, the rust will go with it if you do it right,because of the stronger solution you should rinse with low pressure or you could get the "fuzzies".Just remember the streaks will come back after a few rains so maybe you should prepare your customer for this.
Anyway that's how I would go about it.
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