Pd130 starting problem

[higgster]

Hi guys, my passat is now on 300,000 miles. It is struggling to start either cold or hot.
I'm convinced air is getting in to the fuel system.
So far I have changed
Glow plugs - piece of mind, needed doing anyway
All fuel lines in engine compartment
Fuel filter and manifold on top of filter
Non return valve in supply line
Tandem pump
New battery

Does anyone have a pressure test guide to try to find where the leak is?
Thinking it is possibly injector seals now but don't want to mess with the injectors unless absolutly necessary.
Starter motor seems ok as cranking speed is above 200 rpm.

Really getting to my wits end now.
Any help gratefully achieved as I don't want to retire her yet even with the high mileage.

Cheers