The red damping dial on my shock now refuses to turn in either direction. Played with the 2 small grub screws just behind the dial but to no effect. Help!

pay somebody to fix it

the ball bearing has probably got jammed inside, if it wont move by loosening the grub screw a bit then send it off.

Send it for a service.

Do not take it apart whatever you do! You won't die but when you remove the rebound dial you won't be able to get in again. Not that i've ever done that..no no 😳

There are some pretty small balls and springs to give the nice clicky feel, if they get full of crud they can jam up as mentioned. if you loose them or the springs are rusty the thing just spins around. It is possible to take it apart do it in a washing up basin or similar to avoid loosing small parts.