@imcool great reference work on your battery drain thread
I hadn't seen that till now.
I'm really not technically competent when it comes to electrics, but I have experienced quite a few electrical problems over the years and so I do have a bit of a sixth sense as to what/where I should be looking, but not the technical knowledge to trace a fault such as this one with a multimeter.
If the fault lies in the starter hardware, it must be possible for a qualified auto electrician to use a multimeter to check if there is a high current drain during the cranking sequence.
I have heard in the past of at least one situation on a 12v vehicle where rogue starter hardware was draining down the battery very quickly, but unfortunately, my poor memory isn't helping me to highlight finer points about it. It's just a case of checking through all the elements of the starter circuit.
Relay through to the starter motor itself.

I'm really not technically competent when it comes to electrics, but I have experienced quite a few electrical problems over the years and so I do have a bit of a sixth sense as to what/where I should be looking, but not the technical knowledge to trace a fault such as this one with a multimeter.
If the fault lies in the starter hardware, it must be possible for a qualified auto electrician to use a multimeter to check if there is a high current drain during the cranking sequence.
I have heard in the past of at least one situation on a 12v vehicle where rogue starter hardware was draining down the battery very quickly, but unfortunately, my poor memory isn't helping me to highlight finer points about it. It's just a case of checking through all the elements of the starter circuit.
Relay through to the starter motor itself.