1999 Mazda Protege Suspension Problem

I am hearing a knocking in the rear of my car, the sound is like something rattling in the truck. Is it possible the struts are bad, the right rear strut had a oily substance on it. I have not noticed any bouncing. The struts have never been changed. We will be buying a new car to replace this car in 6 months, is driving this car if it is bad struts a safely hazard

Thanks for your time.

L. T. Coleman