Do you think someones tipped some oil in the tank years back when they knew it would be laid up a while, in a bid to protect it somehow...
They are phasing out all leaded due to lack of demand. practical classics tested the additives you can buy a few months back. The winner was... erm ... erm...
lead
Only problem is you have to buy a large batch of it, bloody brilliant octane booster, so I might be getting a batch when I build my turbo BMW e21 track car up.