I tried all that stuff when I had an remote oil filter line go on my last boat. I must've used 25 gallons of simple green and every other product out there. I spent endless hours trying to get it clean. The problem was that all the soap did the same thing. It lifted the oil, and moved it to another spot.
I finally found the answer, and it was sooooo easy. Powdered dishwasher detergent(, a brush, and HOT water. It ended up taking me 45 min the last time, and it was spotless.
I jacked up the front of the boat on some wood, spun the leg all the way up, and pulled the plug on the back. I spayed HOT, HOT water on a low setting. I sprinkled dishwasher detergent all over, and scrubbed a little bit on stubborn areas. It was really that easy. It all ran out the back into 5 gallon buckets, which I took to the local car wash and dumped into there oil/water separator.
Nothing else even came close to working that good.