79 rabbit

Diesels not running? Check for air in the clear line from the Fuel filter to the IP.
If you are passing air, then you have a leak, the direction of the air leak tells you which part is leaking. From the IP to the filter, then you are looking at the front seal on the ip or the return line from the tank, or an o-ring on the coldt start or fuel shut off.

If it is coming from the filter then you have to verify that the banjo bolts and seals are good, or the fuel line from the tank. Also in the tank there is a pickup screen that can get fouled from old gas as well causing a fuel flow limiting issue.

Loosing prime is quite common condition on crappy running or starting these guys.

The crush washers (copper seals at the banjo-bolts) can be re-used to seal right if you remove them and make sure there are no burs and are flat and shiny. After sanding smooth, hold them over an open flame till they change color from shiny to flat or dull. Let cool and re-use.

I'd first check the fuse, replace the fuel filter, clean or change the injectors, check all glow plugs and replace if needed, check the electrical bar that connects the plugs for corrosion and clean all connections, check the fuel distributor and adjust timing if needed, drain the old fuel and replace with fresh, drain the water accumulator under the car on the passenger side. If you haven't already, pick up a Bentley manual to guide you. In my experience with my 85 Golf diesel it usually is worn out glow plugs that prevent starting and it's corroded electrical connections. I replaced the fuse with a blade type 50 amp with matching holder, makes replacing easier. That should keep you busy!