Might be that the crankcase vent is plugged, that can cause it to burn oil and blow out the oil fill tube,believe I’d check that before tearing it down.If a feller has a second mower to use while that one is being worked on then I would at least see if the cylinder walls are scored and if so I think maybe it’s time to replace the engine or the whole mower if your financial situation will allow it. Remember there is other parts that are probably showing wear after ten years that could start costing you more money. Good luck on whatever you decide. By the way looks like a great place to live there. Wish I could move to a warmer state with less socialist politics.