• If the WD40 doesn't work consider using a penetrating oil, like plusgas, I've found that to work well in the past. I've also used one of those chefs mini-blow torches you can get for caramelising creme brulee to gently heat up both stuck seatposts and pedals to get them out. If both metals have the same degree of thermal expansivity, the wider diameter seat tube will always expand by more than the narrower seatpost, unfortunately aluminium has a higher thermal expansivity than steel, but up to 400°C I don't think it's enough of a difference to cause problems. Not sure I'd have the (bulletproof) balls to follow Bringmyfix's advice, I take my hat off to him.