Fuel line sizes for a 1976 240D (w115) along with some other ?s
 

I just acquired a 1976 240D, and I noticed diesel leaking from the return lines looping between the injectors. The car has sat for quite some time, so I know it will require some maintenance to get it going. I'd like to start by just replacing the fuel hoses all around. Anybody readily know the sizes I will need? I'd like to have it all on hand before I go ripping cutting and pulling. Also, is it common to have the oil cooler leak where the core attaches to the bottom tank of the oil cooler, or is there a more typical leak point that could be repaired without having to replace the whole cooler? Where is the secondary fuel filter? Thank you all in advance!

3.2 mm for those "jumper" lines.

Regular rubber Vacuum Hose only will last several weeks.

Fuel Return Line/Hose size
Diesel Return Hose 3.2 X 1.9 mm For Diesel Injectors (Sold by the
Meter), 240D M616.912-, Brand: Cohline


Where to buy fuel return hose VW RAbbit
Diesel Injector return lines, where to buy? - PeachParts Mercedes ShopForum
The Thread with the part numbers
fuel return line replacement part - PeachParts Mercedes ShopForum

Injector return hose plastic tube
any lawnmower/chainsaw repair shop should have hose that will work too.
I bought a 50' box of 1/8" tygon clear fuel hose and the stuff holds up for about 3 years.
cost me like 15.00
The brand I used is Oregon, it is a Tygon fuel hose.
Tygothane (Saint Gobain is the Manufacturer)
U.S. Plastics is the retailer.

There is other threads.
DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

Thank you, I'll stop by Napa tomorrow to pickup some fuel-safe 3.2mm fuel hose. Now to figure out the Oil Cooler, vacuum pump and dash lights!