The fuel guage on my 91 Legacy is malfunctioning. When the tank is full, the guage works correctly until it reaches the 3/4 mark or so. Then, for awhile, it's most anywhere it wants to be, often plungeing past "empty", floating back up to a half, back to empty ect. Once the tank is down to about 1/4 full(estimated by the trip odometer) it seems to settle down and read accurately again as it heads for true empty.

Not the biggest problem, I can drive with the trip od keeping track, but if theres a simple fix I'd sure like to make this right.

This one is pretty common, my old wagon had it. I didn't bother to fix mine. I just hit the tripometer every time I refueled and kept track that way. Quite a few of the folks fixed theirs. Try hitting "search" for fuel gauge senders. Someone more computer literate than me will probably post a few links.

Most problems like this are caused by dirty contacts on the sender units in the tank. Cleaning the contacts may fix this.