I sincerely doubt dirty motor oil will enhance the floors. Saltillo is very pourous and any oil would penetrate and ruin the tile forever. I renovated over 1000 square feet of saltillo by stripping the old sealer off using a commercial rotary floor machine, black abrasive pad and alkaline wax stripper. As the floor was cleaned, I used clean rinse water to neutralize the stripper and lift the dirt. It takes several passes to get the crud out, and it is a lot of work!

To refinish the floor, I used Tile Sealer 1088 by Roval and freshen up the shine once in a while with their reflecta polish. http://www.roval.com/gloss.htm Mexican tile or saltillo tile must be sealed.

Its a lot of work to clean, and easy to seal and polish. Just be careful that you don't apply things to the floor that will ruin it.