Sand blasting will make a SS surface more susceptible to oil absorption. If some sandblasting was done before the oil contamination, the harder it will be to get out. Try solvent, using the appropriate safety measures.

Oil spot should have been removed prior to sand blasting. Dip the whole thing in oil and wipe it dry. How does it look?

Tool marks may affect reflections as would un-machined vs machined surfaces.

There is (walnut) shell blasting, glass bead blasting, powder blasting. Be very aware of silicosis, which comes from inhaling the dust. Check that your compressor is not spitting oil on the job, a trap or filter is needed.