Thanks for the input. I need a little bit more information here to understand correctly (forgive my ignorance on this).

I thought about fuel pressure bleed-off and did the following test: I turned ignition ON and OFF many times before cranking, which ignite the fuel pump for about 1 second each time, thinking that it will rebuild any pressure loss in the fuel line. Am I right or missing something here?
When doing so, it doesn't change anything to my starting issue, that's why I thought... please help me to understand this probably bad troubleshoot.

Other questions: how would I check for pressure drop? Hooking a pressure gauge to the fuel line? On the distributor? somewhere else?
How can I distinguish between pressure regulator and fuel accumulator, which one is the faulty?

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From 300CE to SLK230K