hi im new to the forums and i dont know too much about diesel engines...
my mom has a 1979 240D automatic trans, in grey and is in good condition. we're the 3rd owners, the 2nd owner was my uncle and he kept it in tip top shape. everything is original. At the moment it does not run. it has not been started for almost 3 years and im pretty sure the battery is dead. b4 the battery died on us, the problem it used to have is:

1)that there is something wrong w/ the instrument cluster (the tachometer, speedometer and the mileage meter) some of them dont even work, only the speedometer worked.

2)another problem it has is that it only goes at like 20-30 mph even when we push on the accelerator all the way.. i just know that we were goin at freeway speeds at one second, then all of a sudden the car slows down... and goes at the crawling speed (20-30mph) then it wont go any higher than that anymore.. (i dont think its the transmission because if it was we would not be able to take the car home...*it took us 3 hrs to get the car home b/c it was travelin 20-30mph)
3) also what fluids do i need to change once the car runs again so that the car would run cleaner, cause i heard that coolant and oil for diesel powered cars are different from Gas powered cars

PLEASE HELP!!! i live in riverside county area (corona area)... so if you can take a look at the vehicle itself that would be very helpful!