Before the ethanol problem, the main concern was that of the misguided withdrawal of leaded fuel from our forecourts. When the environmentalists jumped on the 'lead is bad' bandwagon, worldwide the countries politicians jumped on it too and we were stuck with comparatively poor quality petrol which neither cushioned our valves nor burned particularly well.
The doom-mongers prophesied wrecked head within weeks unless we used expensive LRP or a fuel additive which replaced the missing lead with an alternative valve seat cushion. However, some of us were skeptical and waited to see how it would pan out. Mechanical Armageddon did not appear. What did appear though was a plethora of fuel additives, for which claims of greatness abounded. Various respected bodies undertook long and arduous tests on these and many were found wanting. Castol's Valvemaster and Valvemaster Plus however were given an overwhelming thumbs up. These two additives protect against valve seat recession under all driving conditions, help keep fuel systems clean and protect against corrosion. Valvemaster Plus also provides a good octane boost to unleaded fuel, which reduces pinking, knocking or the need to re-tune or retard the ignition.
What's more, just one milliliter treat one liter of fuel, so a 250ml bottle lasts a good long time. Skeptical or not regarding the valve seat business, there is no doubt that the extra help in the octane department is a boon to the likes of high compression 'classic' sportsters.