I've never used any additive in unleaded petrol either.
I discovered years ago that the Ulster was a couple of seconds quicker up Olivers Mount hill climb on Super unleaded, compared with normal pump petrol. I've used it ever since, and the tank gets drained after every meeting. It goes in either the RL or the lawnmower. That said, I've never had starting problems from using old petrol on any of the other cars.

Thanks for your help

Location: New Forest

Thanks for your information

Location: New Forest

Thanks for your reply it was very helpful

Location: New Forest

Thanks for your information

Location: New Forest

One of my previous Austin 7's handbook (1934 I think) had a detailed paragraph explaining how the new leaded petrol wouldn't do any hard to the engine.
In the 60s I often used Cleveland Discol petrol which had a fairly large ethanol content. The car seemed to like it and ran very smoothly.
I've never had any problems with either alchohol (in petrol) or unleaded.
Originally frequent valve grinding was necessary. Now most(?) cars have had exhaust valve seat inserts fitted because the grinding had worn the seats away. These are likely to be hard and so be in no danger from unleaded fuel.

Many thanks

Location: New Forest

Since lead was eliminated from petrol I have found that no problem arises using modern exhaust valves. When I first started re-grinding valves more than 50 years ago it was common to find bad pitting on seats and even 'flats' on the valve head circumference. If you have a collection of old valves, check them with a magnet. Modern ones are non-magnetic, being made from suitable high grade stainless steel. If they are magnetic they are the old type, and were usable with leaded petrol, but are no longer suitable.

Location: just north of Cambridge