Is WD-40 a good penetrating oil?
“Penetrating” oils and liquids aren’t a very specificially defined category….some are really good and some are just labeled like that and are only a light petrol product with perhaps a little lube added in (like WD-40). The best ones have zero oil in them and are made of chemical esthers and ketones that will really do the job well most of the time. If you bought a good product, then you didn’t waste your money. That doesn’t mean it will work for what you want, however. With relatively tight fits like you find in seatpost/tube mating, if the items have actually rusted, there’s almost no way a penetrant will help. You can try, but be careful with the frame and be prepared to resort to some destructive techniques to remove the old post. You can try to gently spread apart the seat tube clamp bolt eye thingys with a pair of external snap ring pliers (gently…..just a little pressure), and then squirt the oil in. Let it sit for several hours, tap on the post and frame tube with a rubber
