? about rear brake on ttr-125L

The squeak is probably a build up of dust and dirt in the drum or its time for new brake shoes. You dont "oil" them.

Pull out the back wheel and look at the brake hub and shoes. If they are dirty clean them with some brake cleaner you can get from auto parts stores. You can just hose them off with water if you want but dont breath the dust that migt be in there.

If the shoes are worn down new shoes are needed.

You might need a tiny bit of grease on the pivot point if you replace the shoes but no grease or oil should be any where on the shoes or drum. Oiled brakes just wont work.

Good luck and ask if you need more info.