1998 Chevy Astro noises on diffrential

i was driving in expressway all of sudden heard,like the transmission,came off.kept driving till i reached,an auto tire mechanic.he checked say.that the top from the oil cover was missing and lost all oil.i went and bough new iol.and a new cap.after,putting new oil and cap.i still hear a soun.it drives but with a sound.my husband checked under.and says it needs a newfront differential.we have searched the junk yards but no luck.can you help me.wew are stranded.