Q. How do I determine its basis? Do I list what I paid for it in 1972?
A. Yes.
Q. Do I calculate all the repairs, over 50 years, and then subtract all that from the sale price (or add them to the cost basis)?
A. No. You cannot count repairs. You can count "improvements", such as any restoration cost.
Any profit on the sale of personal property is taxed as a capital gain. The sale of a "collectible" is taxed at ordinary income rates (but not more than 28%). For tax purposes, the car you described ("personal vehicle I have had for 50 years" and "a daily driver") is most likely personal property and not a collectible.
