R53 won't start - battery appears fine, absolutely nothing when key turned
I was wondering if anyone could shed any light on my situation before I spend a few quid on the incorrect item.
About a week ago, and this was a one off - the car didn't start when I turned the key. Everything seemed normal; the fuel pump primed, the dash lights came on and subsequently off again, but turn the key to the cranking position and I had a single turn, like the starter firing once, but no crank. I've had a few flat batteries in my time, but this wasn't the same symptoms. Anyway, it had been fine ever since until a really cold night when it did this 3-4 times and then finally gave up and nothing happened after turning the key to firing.
The next morning, I set the car in gear with the ignition on and rocked it back and forth a few times, then it started absolutely fine.
Today it's totally died and nothing I can do will get it to even fire/turn over. The fuel pump primes just fine, and the dash lights up as ever, along with the lights functioning so I am sure it's not the battery/a fuelling issue.
I have checked the terminals on the battery and they are all tight and clean.
Any idea where to look next? I suspect it's the starter motor itself but haven't seen a definitive solution that matches my symptoms. Others have mentioned a new immobiliser box and key reprogram, but surely that would mean I'd never get it started, not just 3-4th time?
Any help would be greatly appreciated.