Car rolling back in while parking on slight slant

It sounds like the emergency brake shoes are worn and need to be replaced. Here is a guide to help you see what you are in for doing the job with diagrams below to show you on your car:

https://www.2carpros.com/articles/parking-brake-shoe-replacement

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken