Hi Rich
THIS link gets you to the instructions for checking tension on a blade stabiliser (near the bottom of page 1). Adjustment as they say is via the large nylok nut on the top - and if you dismantle it altogether by removing that nut, you can replace the friction disks. Beware of cracking the new disk(s) if they aren't properly seated when you re-tighten the nut
Replacement disks can be got from either the manufacturer (e.g. Bulldog) or most caravan accessory dealers - I've always used Towsure in Sheffield.
If you're thinking of a new one, Towsure are offering their Snakemaster one for £70 - I used that model for about 15 years with no problem.
My latest 'van came with an Alko stabiliser built into the hitch - but they're around £300 plus and I'm not convinced they are as effective as the blade type.