Designing Kitchens and Bathrooms - gold stains on porcelain tub after using Tilex

I have a cedar shingle roof that is approximately 3 years old. The color has gone to an ashen grey and the shingles don't repel water like they used to. The roof is in full sun and has no moss problem. I have gotten a couple of comments that it is need of an "oiling" but have gotten vastly different advice on what to use. The Cedar Shake & Shingle Bureau doesn't recommend any product by name but says not to use a preservative. Why not? Any feedback and suggestions on what to use would be greatly appreciated.

I have a porcelain bathtub from the 50's. Every time I use Tilex Mold and Mildew remover (or even a generic mold and mildew remover) on the tile, it runs down off of the tile and leaves dark gold streak stains on the bathtub. I tried bleach and rust stain remover but they didn't work. About the time it starts fading a little its time to use the mold remover again. We don't have a vent in our bathroom so mold builds up easily and the Tilex works great on the tile. Is there anything that will remove the gold stains?