I've just rebuilt my Brompton's rear wheel with a NOS 1975 SA AW hub. The SA shifter works, let's say when it feels like it OK maybe 3 out of 4 shifts. I'm not that fussy, yet. Just wondering if any old friction thumb shifter will do the job ? I have a couple of XTs. I've ridden a friend's Brompton extensively, and know that the SA shifter, even when working properly is going to give my right thumb's muscles some grief ! Thanks.