Subbie1938

I just replaced the oil in the rear diff on my 1992 legacy wagon and used an old 1/2 inch ratchet and jack to remove plugs. Maybe just lucky but no problems. I used the Redline 75/90 synthetic that so many recommended. I was going to change oil in the front diff but when I pulled the little dip stick that is on the right side near firewall it has the red ATF fluid on it. I have the auto trans and thought that the diff would also use the 75/90 oil. I'm sorry but I am a 80 year old idiot and have a problem trying to sort out some problems. My Subbie that I bought used 15 years ago just turned over to 137000 and I try do my own maintenance. Following directions in the Haynes Repair Manual I found the drain plug for the front diff but I don't if I want to drain it until I find out what oil to use. Does the auto transaxle share oil with the diff?