Using the information you have provided and not visually inspecting the roof, the black spots on your roof are more than likely algae. Most shingle manufacturers use copper or zinc coated granules to aid against the growth of algae.
Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil, 2-stroke oil or petroil) is a special type of motor oil intended for use in crankcase compression two-stroke engines.omparing regular lubricating oil with two-stroke oil, the relevant difference is that two-stroke oil must have a much lower ash content. This is required to minimize deposits that tend to form if ash is present in the oil which is burned in the engine's combustion chamber.
Likewise, I wouldn't give a second thought to mixing the last bit of one brand of 2-stroke oil, with a new can of another brand. A similar line of reasoning would be that one cigarette won't give you lung cancer, and one big mac won't give you heart disease.f while it's true that most of the oil samples that get sent out for testing are used oil from a 4-stroke's crank case, to determine the health of the ENGINE, there is no reason you couldn't send out a sample of the oil you intend to use in your 2-stroke to test the health of the OIL.