I have an 8 year old timberframe with a large porch with lots of white oak timbers and tongue-in-grove pine. The wood was treated several times with swedish oil, just like the indoor timbers. Over the years, mildew and dirt attached to the wood. 4 years ago, a bleach solution and power washing did the trick, with oil then reapplied. The mildew and dirt came back much heavier. We have not used the oil since and have tried many chemicals (stripper, restorer, brightener, bleach) and power washing to clean the mildew/dirt, remove the remaining oil and restore the oak to its original appearance -- unsuccessfully (the pine looks pretty good now) -- in preparation for a semi-transparent stain like Sikkens SRD. Any suggestions before I'm forced to spend a couple months with a random orbital sander? The home is in Michigan and the porch faces north. Photos attached. Many thanks.