How do I pass on skills I learned by feel over many years?

You can diagnose almost anything by feel and sound, and that is a lifetime of knowledge living in your hands. Now your body is paying for the years, and you are wondering who will carry the knack when you cannot. That is a real and worthy worry. Knowledge like yours, earned slowly and held in the senses, disappears when its keeper does, unless it is deliberately handed on. The hard truth is that feel does not transfer by feel. You cannot pour it into someone. But you can translate it. When you sense a fault, stop and put words to what your hands and ears just noticed: this hum, that hesitation, this smell. Naming what you know turns instinct into something a younger person can learn. It will feel clumsy at first, because you are describing what you normally just know. Do it anyway. Find one person worth teaching and let them work beside you, and each time your instinct fires, say out loud what you noticed and why. You will not transfer it all. But the part you put into words outlives you, and that is how a craft survives. Your knowledge is worth that effort.