These return lines are exposed to a lot of heat, vibration and diesel fuel, which nowadays could have additives or even be a more environmentally friendly fuel like biodiesel or renewable diesel of some form.
From time to time you're going to need to replace them. It is easy enough to do, and can prevent a big mess if you replace them before they start leaking like mine did.

➡Here are the replacement lines I used: https://amzn.to/43xMPek

0:00 Intro
2:08 Remove old lines
2:57 New plug
3:39 Install new lines
4:57 Check for leaks
6:05 Diesel sprinkler gone

Become a channel member to get early access to videos and help support what I do:
   / @trythistv  

(links on this channel may be affiliate links, which earn me a commission upon a qualifying purchase at no additional cost to you)