FCP is the best place to purchase oil. They have a lifetime warranty on all of their products. I'm not being condescending, I just want to make sure I am being clear and therefore I have spelled out all of the steps below.
1)You pay for the oil.
2)They ship it to you.
3)You put the oil in your car.
4)You drive the car.
5)When you are ready for an oil change you order/pay for new oil.
6)They ship it to you.
7)You remove your old oil and ship it back to them including filter and gaskets.
8)Once received they reimburse you for the payment you just made for this batch of oil.
9)Rinse and repeat.
You literally pay for oil, filter and gaskets one time and you have a lifetime supply of it. It's that simple and easy. They even have a how to video on their website. The only question would be can you change the oil yourself. The answer is yes. There are a few steps involved but it is painless and fun.
https://www.fcpeuro.com/products/bmw-oil-change-kit-e9x-m3-tws-11427837997kit
https://www.fcpeuro.com/page/lifetime-guarantee