I'm having a heck of a time with the oil and viengar dressing I take for my lunchtime salad. No matter what type of container I take the dressing mix in, the oil finds a way to seep out under the seal. I've tried various Tupperware and Tupperware look alikes, baby food jars, and small mason jars with no luck. The containers don't leak for anything else, just oil and vinegar dressing.

Has anyone found something leak proof?