Shado

I have an 81 300D with a cracked radiator. Everywhere I go for a replacement has a unit that uses an expansion tank to fill the system. The one in my car has a filler neck with cap and a simple overflow hose similar to what I find in an 80 240D. It's been replaced at some point in it's life because the one in my car is a Holland brand, but I can't read the part number. Are these actually interchangeable?

rocky raccoon

You can backfit a later W123 radiator and expansion tank to your car. In fact, you will probably find pre-existing holes in the passenger-side inner fender to accommodate the tank mounting. I recommend a Nissens radiator. It is a Danish company that makes radiators for our old cars. Better quality than the original I think.