Thanks for reminding me of this post. I can update with some new info..
Since my overflowing carburettor debarcle from a year or so back, I have been using a Millers additive with my fuel:
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Amongst it's claims is protection of traditional rubber seals in the fuel system from the corrosive effects of E5 & E10 fuel. I can't verify this as yet, but I would say I have noticed a difference from when I put the additive in to when I don't. They are only small differences but do make a difference, for example:
1: Much quicker on re-start when engine is up to working temperature and has been left off for 10 minutes, or more.
2: Tick-over and general engine sound is smoother
3: There is a definite improvement in pulling power, it's more eager (as eager as a 2.25 Land Rover petrol engine can be
)
4: The fuel does not 'boil over' as readily in the carburettor after a run and the engine has been left off for 10 minutes or more .
So I will continue to use this, there is a noticeable difference when I forget to add it when fuelling up, I would recommend this.