If I read your post correctly, after you crimped the line, you awoke to no bubble. That means you have no leaks after the crimp, on the engine compartment side. The leak is before the crimp, on the tank side. That's why I suggested you move the crimp one step closer to the tank, to see if the leak in the steel supply line or after that. The supply line is the one that goes to the fuel strainer.

If the clear line is 5/16 i.d. I would not trust it not to blow when the engine gets hot. If 1/4 " i.d. I'd trust it for short term.

Edit: I see you have no clamps on the clear line. Air can get in on the relaxation stroke of the lift pump when it is under vacuum. I already explained to you how to make a clamp with rubber band.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Yeah, apologies this part me be unclear. I haven't isolated the primary filter, that's what I'm trying to express. I pinched the line *directly* before the lift pump so I'll be working backwards, section by section. I'm not convinced just yet that the primary filter isn't the problem.

Edit: the clear line i installed was the 1/4 and boy was it a snug fit. I can certainly wrap some rubber bands around it but to be honest I'm more concerned about when I have to remove it.

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1981 240D 4sp manual. Ivory White.

You remove it the same way you installed it. Microwave a cup of boiling water and slowly pour it over the tubing to soften. Yank it off with a pair of pliers.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked