I am looking to learn about outboards by rebuilding one. I found a mid 80's Mercury 115 with tilt and controls for $300. Seller tells me one cylinder has zero compression, the others have good compression. The motor looks complete and is not in a position to do any further checking other than visual. Knowing I will to do a full rebuild, my questions are ... is $300 reasonable ... (sounds reasonable to me)? What else can I or should I check and/or look for without being able to crank or spin it?