My issue is that I fill me tank and the gauge shows zero, then after about 100miles it will shoot up to showing full. then it will slowly go down with the fuel being used, but not an accurate indication of the fuel in the tank. I dont think its the needle as it moves freely but the fuel sender unit in the tank.
I know this is common problem on the CLK, as I have the posts . Can someone tell me how easy is it to get the fuel sender unit out from the fueltank, is it underneath? is it straight forward to do? photos would be great.

PS I have had this problem before and managed to fix it with fuel injection cleaner liquid you put in the tank, but this time it hasnt worked, although its only been 3 days since my problem.

Thanks