Does anyone know how to get dried, oil base paint out of a t-shirt?

If those didn't work, try the solvent mentioned on the paint can.

https://home.howstuffworks.com/home-improvement/household-hints-tips/cleaning-organizing/how-to-get-paint-out-of-clothes2.htm

Use turpentine or mineral spirits and try soaking the spot for several minutes to hours. You need to use the solvent/thinner for the paint.

Try a dab of hydrogen peroxide mixed with blue dawn dish soap

Try paint thinner for oil based paints. Soak the spot for at least an hour or two. Good luck.

Try this website. Scroll down to find the part you need. Keep scrolling when you find the part that says "Read More Below"

https://www.persil.com/uk/laundry/laundry-tips/stains/how-to-get-paint-out-of-clothes.html

Good luck!

I have used lacquer thinner with fair results

Dirt Devil stain remover..........

Does the T-shirt have sentimental value or did you pay a mint for it? I'd just toss and replace. My husband was on sea duty when I had our first child. He got leave and came home to see the baby--I was living with my parents at the time. The day before he came home he went to his aunt's house and helped her husband paint. Then he very kindly and considerately brought the paint-stained clothes home for me to wash. Words were had, but I did wash them and they came out fairly clean.

Good luck! I can see why this one matters.