P&H Skeg Maintenance Kit - Low Friction Yellow Cord and tiny bungee. This is the current factory replacement cord for P&H kayaks with a string and bungee style skeg or "skudder" control system.

Note the current production string (yellow or red) is thicker than the blue string that the earlier versions of these skeg systems were designed for.

P&H hasn't stocked the blue thinner line in a while.
P&H changed the skeg line to the thicker yellow one a few years back (2019?). With the MKII slider system it is fairly easy to remove the slider knob and drill out the hole in the aft end of the control box just a bit wider for the yellow or red string. If you still have the original version of the slider assembly you could try to widening the hole on the button the line goes through or you can replace it with the MKII slider knob. The easiest way to distinguish between the original control box and the MKII is that the MKII slider assembly has two silver colored Allen screws at the front of the assembly.

2022: Some P&H sea kayaks came with a red cord. P&H has had trouble sourcing the yellow cords this past year and has moved to the red. Should be no difference at all - depending on who you ask the red is either better or exactly the same.