Also, I did buy my washers from the cummins dealer. But no o-rings came with the injectors...it is a 12v if that makes a difference

 

You dont have the rubber o-rings. Just the coppers under the injector and the ones on the return line. I would pull the leaky injector and make sue the bore is clean and that there arent two coppers stacked up or something easy like that.
Which coppers did you use, there are three different thicknesses (sp?).

 

NOTE:Washer thickness varies, depending upon diameter of the injector tip, CPL number and part number stamped onto the injector body. Measure thickness of an original washer and replace it with one of the same thickness. If an old washer is not available, consult a dealer parts department for necessary information.

Ok this is a quote from my Haynes repair manual. Of course they are speaking of replacing stock injectors. But it makes me think and makes me ask, "are aftermarket injectors any different?". Do after market injector tips diameters vary as much as stock tips do? If so, do you have the correct washers for your after market injectors?

 

Do I need to worry about gettin fuel into my oil on a 12v?

 

Not from an external leak (return line or feed line) as long as the coppers are sealed. If the coppers arent sealed good an exteral leak could get to the oil. (Not likely). Keep an eye on you oil though, I could be wrong.