1- The cruise control problem is probably the amplifier, which is a common problem. A rebuilt amp is about $175, easy to change, located above the driver's feet behind the trim panels.
2- 35mpg is good for this car and with a light foot might do even better!
And Larry, the W124 E300D does indeed have a 90L (23.8gal) tank, no larger. The only other W124 to have a 90L tank is the 500E, all others have 70L (18.5gal).
3- Tim, the E300D is fast compared to any other diesel except the 98/99 turbos. It has 134hp, normally aspirated, and goes 0-60 in roughly 12 seconds. There are zero performance mods possible with this engine however, so you better like it "as-is" and don't expect to get more. NONE have manual transmissions!! Period! No W124 or W210 ever came to the USA with a diesel engine and a stick shift (in 86/87 you could special order a 30E gasser with a 5-speed but those are very, very rare.)
4- Chris, how do you like the 500E? I've been dreaming about one for a long time, but all the "nice" examples are either the wrong color, too expensive ($25k+), or both! What kind of MPG do you get on yours?
Regards,