onions are commercially grown in muck soils and they often ooze when the tops are cut . You are just seing the plnts normal growth and fluids , so I wouldnt worry unless the plnt smells like its rotting (too much moisture can induce rot and molds in onions).
We grow a small kitchen garden near the house with herbs and "bunching" onions that we use for scallions and green onion slices. I also grow garlic and we are about ready to pick this years garlic. (I plant garlic in September and harvest it in June--oterwise it doesnt produce big bulbs)