88 300CE overnight can't start engine

There's a relay that powers the fuel pump: i.e. fuel pump relay, that often first becomes intermittent, causing hard starting and stalling underway, yours probably died, R.I.P.

Update: I have taken apart the distributor and found carbon deposit. I tried to sand off the deposit and put back the disbributor but it didn't help. I ended up taken the car to pepboys and after $382 my car is running fine now/. The problem: bad distributor and the rotating head. I quess they just worn out and not the deposit.

You already had it off, you could've saved yourself 200 bucks and did it yourself.

Sanding isn't a good idea as it actually removes material and the gap is important in this case... using a solvent like water or alcohol to remove gunk and then drying totally is a better approach.

Oh, glad it's fixed anyhow. You were awfully close! Usually replacing the cap and rotor is a better idea then trying to refurb them, as these parts do wear.

Marty