The green thingy.
nectar, got you started right. Use oven cleaner to get the carbon off. The green thingy is normally called a Scotch Bright pad. They come in different coarseness and there are different brands other than Scotch Bright. From your description it sounds like the rings were worn out and allowing a lot of blow-by down the cylinder wall. You might want to have your local dealer check the cylinder to see if its worn out and needs replaced or redone. But, what you can do is get a new stock piston ring and find out what the limits are for ring end gap. Clean the brown off the cylinder wall and put some light oil on it. Push the single ring in with the piston (note clean piston first). Start at the top of the cylinder and then push the ring down the cylinder at 3/4 inch intervals the full length of it and measure the ring end gap each time. If the end gap is beyond spec, the cylinder needs to be redone. When done, wash everything with warm soapy water and rinse well with fresh water.