86' 300E erratic fuel gauge

First I would like to thank you guys for your help W/ valve guides. I have this problem with my fuel gauge, the first 1/2 seems to register fine , but once below that it's all over between 1/4-1/2 mark, when I get down to about 2-3 gallons, the gauge wanders between R-1/4 somtimes as much as 1/3, I have replaced the sending unit,seemed to help a little but not fixed. I have the Electric trouble shoot manual but can't really determine what could cause the gauge to move all over the place, any ideas? Grounds? bad gauge? I did"nt see a voltage reg. for the insturment cluster, I guess MB doesnt use one,like old American cars had.
Thanks again Chris C.

I have seen many faulty fuel gauge assy's. Also I have seen the screws that hold the gauge assy's together in the cluster loose (they provide the ground on the chasis of the gauge in a series). Do check to see that the wires from the sending unit all have very little resistance from one end to the other. Also be sure that the ground going from the transmission to the body is in place.

IF THE NEW SENDING UNIT DIDNT FIX YOUR PROBLEM THEN THE GUAGE CLUSTER MUST BE AT FAULT. THE SENDING UNIT IS ONLY A VARIBLE RESISTOR, STARTS AT ABOUT 80 OHMS & GOES TO ABOUT 3 OHMS.