I've never replaced mine, although they have stopped working a couple of times. The problem with them, is that there is virtually no play in the joints when they are new. Only a small amount of corrosion is needed for them to sieze up. The trick is to remove them completely, and free all the pivot points completely, so they're quite sloppy. The sloppier the better. Mix a little HMP grease with petrol to lubricate and protect the pivots, wipe off any surplus and refit. I don't think there's any permanent solution unless they were replaced by ones made from stainless steel, but I guarantee that after the above treatment, they'll last much longer than new ones before they sieze again.
Snap! I used the same method. I also used to remove the pin ended screws that located the non moving pad. The ones the book said not to remove. :-) It made the job so much easier. I still have the special Girling tool for winding the adjusters back. Not that it was much good in any case. Using it was a pain.
I must be lucky again. None of my cars have ever suffered from fuel evaporation. Mike.