What's your tipple?
Whatever its virtues or otherwise, unleaded petrol had expensive effects on aviation as well. From around the mid-60s (I think - usual memory caveats) we used 80-octane and 100LL, supposedly Low Lead. The 80 stuff was used in the Gipsy Majors (TM, Auster, Chipmunk) and low-powered Continentals/RR in C150s etc while the 100LL was to the liking of Lycomings and would you believe Merlins? When Spitfires came on display visits they quenched their awesome thirst with 100LL apparently without harmful effect except to the bank account.
Today's Avgas has no lead content and soon knackered the valve seats on early 1a Gipsies with bronze heads, the later 1c having aluminium heads with steel seats and slightly more power. The solution was to fit 1c heads at an expense you can guess at. The Chippy has Major 10 with alloy heads and some 20% more power so I think was OK. Maybe Smudge can remember more?