i have the EXACT same problem with my '77 240D. the meter reads well intil it hits about 1/2 full, then i notice that it will sit on 1/2 for a few days, then it will dip, dive, shake, and shoot back and forth from 1/2 to R (never all the way to empty). the only difference is that my reserve light never comes on. maybe my bulb is out, or maybe my gauge is in even worse repair than yours. do the needle and the reserve bulb work with different sending units/sensors? i was thinking about taking out the sending unit for inspection....... can anyone offer any sound advice on the issue?