Ok so I own a 87 rx7 gxl and as I was doing my routine oil change when I noticed that my diff wet. As went under for a closer look I saw that the front part of the diff, which connects to the drive-shaft seems to be leaking cause the is fluid residue. So my concern is how can I fix this problem? Is it just a seal I need to replace?

 

Thats the input shaft seal. I don't know the procedure for replacing it since you would need to remove the flange / shaft coming out the front and I recall there being a special spacer in there that may or may not be re-usable, but if you can find the procedure and nothing else is required it should be a ~$5/part and 2-3 hours (as you will probably have to drop the catback part of the exhaust to get the driveshaft out of the way).