If one gets a drop of rainwater inside the fuel tank, it attracts the ethanol out of the fuel. This mix becomes very acidic, and, since petrol floats on top of water, the aicdc droplets are trapped at the bottom of tanks, or float chambers. They then eat away at the steel or alloy. Answer is , to be very careful not to get water in the fuel tank.
It appears there is much hypothesis about the effects of ethanol on old technology engines.
However, Manchester University undertook a series of thorough tests, using a very old technology engine as a guinea pig [MG XPAG, to be precise].
The results are quite surprising.
These can be found, in depth, in the following publication [and is supported by the FBHVC].
https://www.veloce.co.uk/store/Classic-Engines-Modern-Fuel-The-Problems-the-Solutions-p151478624This book can be found cheaper in the usual sources.
It does not purport to be a holier-than-thou production, but the presentation of the results of the tests, in an understandable format...with one or two suggestions, which are not claimed to work in every instance.
Regarding the degradation of fuel systems apparently by ethanol [but some other of the additives may well be culprits as well?].....the point is made that, if one is running around in one's ''classic'' still with the original rubber hoses, gaskets, etc..then isn't it really about time one replaced all these??
For some time now, rubber {?} hoses, etc have been ethanol-proof anyway. {Unless buying cheaply off tinternet?}
The one surprising outcome of these tests was, ethanol actually improves the running of old technology engines.
For sure, ethanol is oxygen-rich, therefore will tend to make older engines run slightly weak.....if an issue, then 50 quid on a rolling road will show how much the main jets need to be drilled out? However, because of an engine-running issue known as 'cyclic variability'....which, on old technology engines actually creates much hotter exhaust gases,using as we must, today's petrol......[which is totally different in composition to petrol sold in the 70's and 80's!].........then, because the addition of ethanol actually reduces the adverse effects of cyclic variability, engines may well run cooler.
Evidence Of the improvement in running offered by ethanol, is also present to any really old fahrt drives, who would have been running around in the 1950's and 1960's.......Cleveland Discol, anybody?
??
Today's petrol doesn't have any adverse effect on modern engine designs simply because of the computerised engine management systems commonly employed..these compensate accordingly.
Anyhow...don't necessarily believe urban myth regarding ethanol.......get the book, study the results, you may be surprised......and keep rainwater out of the fuel system!!