I got a sensor set up last year and it's great. You need a raspberry pi with a camera.
https://github.com/tangentaudio/opencv_tank_gauge
The project includes all sorts of 3D printed goodies that I skipped. Since it's optical in nature, the readings change if there's a change in lighting (garage door open, etc). I just painted the inside of a cardboard box matte black and covered the whole thing. Works great.
Another thing I did differently is I used an IR camera. The project is designed around normal cameras. There's a closed issue on GitHub where I figure out the settings to change, so you can check that out if you want.
It feeds into Home Assistant and I get notified when the oil is low, can look at graphs, etc.