I have a 2000 dodge Cummins with 240,000 miles on it.
For the past year or so it starts really slow.

After it sits not running for more than a few hours it turns over for a very long time before it fires.

Not really a big deal but my remote start doesn’t work when it does this. When it first started happening I was told by a mechanic that it was a small leak in an o-ring in the return fuel line. I never received the part from him and really would like to fix it.

Does anyone have an idea if he was on the right track and when this is located? Or maybe give me another suggestion how to fix it.

I have run an aftermarket Lift pump, Injector pump and injectors incase that matters.

Thanks for anyt Info you have.