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The engine will start OK as long as one or two cylinders have decent compression. Low oil pressure is the result of oil pump and bearing wear, and is unrelated to cylinder sealing. Have you checked your compression tester? Perhaps the guage is inaccurate. Try it on a car, or borrow another guage. A leak-down tester (aka aircraft compression tester) would be a good way to track down issues with #1. They are also a more accurate way to evaluate cylinder sealing. You could approximate a leakdown tester the following way. Position the engine to #1 TDC on compression stroke. Put the tractor in high gear. Pressurize #1 cyliner to 80 PSI or so with shop air, using a fabricated spark plug adapter or a rubber-nosed blow gun. Listen at the carb air horn, the exhaust pipe, and the oil breather pipe for the hiss of escaping air. Some sound at the breather pipe is normal ring leakage, but any sound at the exhaust pipe or carb horn corresponds to a leaking valve which should be fixed.
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