I got one Dahon Speed cheap, it was a good price and when I met the seller, a trucker, it had a HUGE hole worn in the side of the seatpost, and Dahon seatposts are pretty thick wall and good aluminum. Must have been stored alongside something steel, like chain tie-downs or something. He agreed to cut the price of the cost of a new seat tube. Better a replaceable part like that and not the frame. That bike came in handly when my Speed frame cracked due to the early plastic seat-tube/post bushing, and I didn't catch it early enough to mitigate the crack. When I finally did my 2X crank upgrade and overhaul (by which time the cracks had migrated back to the seatstays and down the seat tube, that triggered the upgrade), I swapped out the frame. The old cracked frame plus spare fork, I use, held in a Workmate copy, as a wheel truing jig.