Its probably the drive flanges. Mine on my '87 are doing the same thing.
Its not hard to replace them. Remove the drive axles and you'll see a plastic cap on the inside center of the drive flange. Remove it with a small screw driver. Don't worry about destroying it, you'll get a new one in the seal kit. Behind that is a snap ring, remove it. You should get a new one with the kit as well. Becareful, the flange may pop out at you. There is a spring behind it. Pry out the seal and replace it. Installation is the reverse.
The tricky part come when you put the flange back on. The spring needs to be compressed so you can install the snap ring. There is a special tool that makes the job easier. Its possible to do the job without it, but it makes it a whole lot easier.
You may be able to make a tool. Its basically a long bolt and a piece of flat steel. There is a threaded hole in the middle of the output shaft. The bolt or even some threaded rod goes in there. The flat steel has a hole in the and its large enough to cover the flange edges. Good luck.
