Son drove home from college today and said the transmission had been shifting strangely the past few weeks. I warmed up the car put in neutral and checked the fluid. It was low. I added about 20 ounces of ATF, drove it around for a few minutes, back into neutral. Son checked it this time and level was at the "add 1 pint" mark. He added a pint (16 oz.) of ATF, drove it around, back into neutral, checked again. Still showing to be at the "add 1 pint" mark. While wanting this to be teaching moment, also don't want to over-fill the transmission, not sure how much more it needs before it hits the full mark. Please advise.