Misfire - Coils & Plugs

[UKE60EA]

2006 M5, around 60,000 miles. BMW extended warranty (probably not great for disposable items). Owned since around 15,000 miles/2008.
FBMWSH
Used very little this year, recently misfired on start, but once warm, no misfire. Also showed low coolant the day after topping up.
Took to a main dealer (new area/dealer for me), who said coolant sensor fault, and that one of the spark plugs and coils needed replacement. Approved. (£150 plug/coil/labour, plus the fault finding fee of £125).
He called back to say another plug/coil showing misfire fault, and that when replaced, yet another cylinder now showed a fault. He said it might be because the fuel was low, and that when it gets low, the car starts to shut down injectors (something I’ve never experienced) and that it might be a sensor fault, so they added more petrol. No change.
He asked if he should just replace all the plugs/coils, or do it one by one.
It sounds strange that a fault would only appear on each other cylinder when fixed on a different cylinder, rather than all show up at once. There are a couple of independent BMW specialists near me in East Anglia – maybe it’s time to leave the main dealer and try people who might be more familiar with cars of this age? Or do I just get all the coils/plugs replaced?

[M5Rick]

This can also happen with F10's,always refuel when gauge shows 1/4 tank. Appears one prob is following another in some sort of 'sympathy'.It is a V10 so maybe a diagnostic at an older M specialist may pinpoint what's causing it to chain react because it's strange one thing should follow another. Good luck!
*Oh nearly forgot, first thing to do is clean the Mass Air Flow sensors with special spray only if they haven't been touched for a while.

[UKE60EA]

My follow-up didn't get posted?
The dealer seemed unaware that we had a BMW extended warranty - it's usually flagged up when they enter the registration. When we reminded him, he suddenly felt we only needed to replace the two currently-prompted coils etc, saying that the criteria for replacement are 'different' under warranty... I had the feeling even he wasn't convinced by his answer.
Replaced, and no problems since. If more coils were needed later, we would have had an interesting discussion about whether they wanted us to pay another excess.
Thanks.

[Taheemr]

Had this issue too, cleared it self after a good blast, so put down to crap fuel, having said that it does idle slightly indifferently from time to time

[M5Rick]

Use red redex with Momentum99.
Switched over once to v-power and a CEL came up, that fuel has too much detergent in it so cleared and went back to Momentum.The car don't miss a beat, no shaking on start up and smooth tickover always.