According to Brompton there are 2x ways to replace the sleeve:
Or…. drumroll please - option 3, print your own, clip it in and off you go…
Been rocking PETG printed sleeve for more than a year now (clocked in 4k miles = 26miles a day, 4x days a week x 10month) and it started slipping lately, oh yeah I'm little over 100kg.
Was trying to do PLA but after 2x weeks it started delaminating, upped to PETG and no issues what so ever.
Included 2x sizes, 0.5mm difference on internal diameter but makes all the difference. Would suggest to go with tight 1st, Brompton frame does not like too much flexing so tighter better.
The author marked this model as their own original creation.