I agree with Doug. Be sure that any residual chemicals are completely removed from the surface of the image. I have not used either the PEC-12 or OOPS and I don't have any idea if they have been tested for long term effects. Sometimes residual chemicals won't harm the surface initially but over many years changes will occur. The easilest example I can give is finger prints on a photographic emulsion. Initially there is no sign of damage but over the years the oils left on the surface will discolor the image and the finger print will become visible. Oh, always use the least harmful products first so in this case try water on a q-tip before you jump to other solvents. Just be careful and as Jim said use it sparingly and test test test!
Tudhope Conservation Studio