I admit defeat - after messing around for ages, following instructions in my user manual, carefully winding new line onto my old spool and after finally getting it done, finding my Reflex won't auto-feed. Thinking I'd done something wrong I then took it all off and wound it all again still finishing up with the same result. I've now come to the conclusion it's just not worth it!
Replacement line may be a bit more expensive this way, but having tried the above and failing miserably, I then bought one of these - it just slotted in, no hassle, no messing. This is what I'll be buying in the future.