I've a '90 124128 with the"602"

That would (I believe) be your "Fuel Warmer".The two hoses that leave and
disappear around the back side of the oil filter housing should connect with
the engine cooling circuit; when the engine reaches operating temp heating
the fuel.

The plastic you see may be your problem.You can run the feed
line directly to the mechanical lift pump on the side of the injection pump.
It is oriented perpendicularly to the engine Driveshaft and has two hoses.
If you do decide to try this as a "temporary" fix ,remember to place a
primary (Little Plastic) fuel filter in between the tank (metal) supply line
and your lift pump.The second hose leaves the lift pump and connects directly
with the secondary (spin on) fuel filter.