No motor oil. Nasty stuff. Bad chemicals and it will never cure.
Seal the ends of the slabs, then stack with stickers and dry. The go to the finishing.
Sand the wood properly. Better yet is to plane then sand.
Oil finish, Teak sealer first then Teak finish. I put on 3 coats of sealer, drying between each coat, then 6 coats of the Teak oil, drying between each coat.
Before, hatch on my Mako 22 foot Center Console boat:
Seafin Ship N Shore is Teak sealer.
After. Wood is Teak.
Or a good brew of Linseed oil and dryers. Or Shingle oil. Or a good deck sealer oil. Use your stain of choice prior to the oil. Raw linseed oil takes forever to dry, maybe never here in the damp Northwest.
Indoors, clear or satin Spar Varnish.
Below is a test piece of Pacific Bigleaf Maple about 3 inches wide. With a stain "brew" of mine and 20 hand rubbed coats of Plinkington's gun stock oil.
The maple was white like the blanks in the below photo prior to finishing.