Injector cleaner won't help and is actually bad for the system as it can dislodge gunk and block up your fuel filter or worse.

A glow plug controller will show in diagnostics as all 6 plugs being faulty. Individual plugs will return individual codes. Very rare for all 6 plugs to fail at the same time so if you get that code, replace the controller. Unfortunately it's in a bugger of a spot under the manifold which is often why people do it all at the same time.

Manifold gasket should be ok if it was only replaced recently.

I think that your issue may be injector related. Could be an injector leaking or dribbling once the car is shut off, loading up the cylinder with diesel, making it hard to start until it clears. Kinda like flooding an old carbureted motor.

Try this - park the car on a steep incline with the nose of the car point downhill. Try the same the next day with the car pointing up hill. If it's easier to start on day 2, it's a good way to diagnose that an injector is flooding the cylinder.


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