Would mucus in stool that comes and goes for a bit every few months be a symptom of colon cancer? no other symptoms. no blood that can see.

Unlikely: Mucus is not suggestive of cancer. Unless you have family history of early onset colon cancer, you may wait till you are 50-years old to get a screening colonoscopy. If you are concerned you may do FIT testing to test for occult blood in stool. If that is positive, you should see a doctor. Wish you good health. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex.