They are a real pain as they are located on the clutch peddle, so the only way to work on them us upside down laying on the front seat.The best advice I can give you is to inspect them to see if there is any damage to the teeth on the half round gear, if there is buy a complete set from your local ford dealership. It should cost no more than £30 for the complete set.
Even so, I'd try adjusting the clutch
The adjust mechanism consists of a spring loaded ratchet quadrant attached to the clutch cable. To aadjsut the cable, grasp clutch pedal and pull upward, then slowly depress clutch pedal. If a click is heard during the procedure, an adjustment was necessary and has been accomplished. This procedure should be performed at least every 5000 miles.
If there is no click, the cable is as tight as it needs to be -- so any slippage would be in the clutch itself.
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If you want to do it yourself, here's the basic procedure:
Replacing a Clutch:
1. Remove transaxle (engine must be supported from above with fender braces or an engine puller).
2. Loosen pressure plate cover attaching bolts around clutch cover.
3. Remove pressure plate and clutch disc from flywheel.
4. Position the new clutch disc and pressure plate onto flywheel with flatter side of clutch disc facing toward flywheel. Use a pilot tool to center the clutch disc on the flywheel.
5. Ensure three dowel pins on flywheel are aligned with dowel pins on pressure plate.
6. Tighten the bolts on the clutch cover evenly in a star pattern so as not to distort the clutch. Then final tighten the bolts to 12-24 ft lbs (17-32 Nm) .
7. Remove alignment tool, then install transaxle and perform initial clutch adjustment.