xperience shows me what you get from Service stations is pot luck and pretty common to get bad batch.
There are some other threads where Jabawocky and I have debated this in detail, but I maintain the Australian refined fuel has quite good "batch control".
The bigger problem issues are:
1. companies who import fuel bought on the international spot market
2. service station sites adding cheapening chemicals
3. Service station sites with old ingound tanks which let in contaminants
If you are going to use Mogas stick to 98 octane fuel from a high volume Shell, BP or Mobil site. These are the only companies who refine in Australia and therefore have a consistent supply line. All other service station brands are buying fuel from somewhere else that is unknown.