Hi jtwmc,
I agree with gordon, spray over previous coating is never recommended. BUT...if the "circumstances" are such that you donot have enuf time and you have to return it urgently AND if you do think of spraying over the previous coating make sure you do the following things:
1) Clean the job thoroughly with solvent
2) Ensure that you have good surface roughness (atleast 6 Ra micron)
3) IMP* before you spray give atleast 4 to 6 passes of preheating at normal coating speed. this will ensure that "most" of the oil seeps out and vaporises.
4) then spray without over heating the job ( not more than 100DegC)
All the Best!!