I use a foam brush to stain the teak, it keeps the stain from getting streaks. The foam brush also allows the stain to fit into deeper spots and between the louvers. I would recommend sanding as much of the black out of the teak as you can before you stain. The stain will not really bring the color back out of the wood, it will seal over the black, it will blend it in better then teak oil or how it may look now, but the only way to eliminate it is to sand it out. I used a thin piece of plastic as a sanding block, it would get very close to the corner of the louvers, probably within 1/8" or less from the corner. I have not had the black reappear since I switched to the sikkens cetol. I used the matte finish to make it look like raw teak from a distance and even up close, there is a gloss also, but I thought it would ruin the look of teak and make it look like any other wood. I used the light stain, as you apply more coats it will get slightly darker, usually 2 coats are enough and will last you 2-3 years, likely more for the cabin door and spots that are not as open to the elements that that cockpit teak will endure.