Bluenote: good tip, though I have used 3 different SR stems on mine and all have gone in without issue - perhaps enough wear after 40 years?

Also for those new to AO/UO-8s: you may find a spacer in the seat tube to let the original steel seatpost fit - you can take it out to allow a greater option of sizes: again I have sourced several different posts from the local used parts emporium that fit without issue - current post is an SR LaPrade...

Mark