It was the old Jag that needed a new slave all those years ago.
Fortunately I’ve not had to replace one on an MX5, modern materials and modern fluids are much better. BUT the fluid requires regular maintenance, because it is hygroscopic and will absorb water vapour from the air. On these MX5s it should be replaced every two years, regardless of mileage.
If the outside of the slave is clean and dry of any fluid, it is not leaking and therefore highly unlikely to be faulty.
Bleed the slave first; this is easy if you are happy crawling around under cars AND have the right kit AND know what you are doing. Otherwise ask a professional.
Being old and creaky now, I normally ask for it to be done at a service when the car is up on a lift, then it’s only a five minute job for the garage while they bleed the brakes.
The clutch master cylinder shares its fluid reservoir with the brakes, and you must use the correct brake fluid (ALWAYS use a new sealed can/bottle of DOT3 or DOT4). Old fluid can compromise braking and clutch operation.
After correctly adjusting the pedal end of the system, its operation was still inadequate and the next service and MOT is not due for months. Therefore I had no choice and I bled the 25AE clutch slave myself. Problem solved.
I suspect the fluid in the slave might have been nine years old because some dealers tend to overlook it when they change the brake fluid.
Shifter turret uses gearbox oil, and yours should not need touching unless the mileage is excessive.