Hi Grumbleweed
I can`t see a connection between the Tacho and the timing belt because the signal comes out of the transfer gearbox.
If you unscrew the "cable" (it is mechanical Tacho) as you see on the picture from a L200 and see if there is some wear.
on L200 it is normal to have a swinging needle on the Tacho when you drive with low speed, sometimes it swings between 10 and 30 kph when you
drive on 20 khp.
The slave cylinder is sometimes a problem on the mitsus, I lost it twice because the piston just fell out of the cylinder.
If you go offroad, and get stuck in sand or mud the sealing breakes and the dirt will go between cylinder and piston and then the slave cylinder is gone.
A autback repair is to change the break fluid to a gear oil or equal fluids.
You`ll have a different feeling, and the clutch is harder to press but you can go on.