Found this on the internet, it may be helpful.
'Ladder and Step Ladder Repairs
In the majority of cases most ladders cannot be repaired as doing so may invalidate their compliance with the standard in which they were certified to. This is why any repair should be carried out by a qualified person to ensure the repair work conforms to that standard. If a repair is carried out to an unacceptable standard then you would be liable for any potential claims against you for the ladders no longer being certifiable.
In those cases where the ladders can be repaired it might not be cost effective to do so and may actually be cheaper to replace them. For example, if the aluminium rung needs replacing then this will involve separating the rung from the stile, welding in a new section then re-certifying it; the labour cost and time involved may cost more than a replacement ladder. If any damage is caused to the stile then the whole stile would need replacing as the inegrity of the entire ladder could be compromised with a localised repair.
For these reasons we recommend that if a ladder is damaged then the whole ladder should be replaced. However, in saying that, with the proper care most ladders go on for years of use without any problems at all.
The same concept applies to step ladders as the production of the steps is similar to that for ladders. However, on some step ladders that have a platform step it may be possible to replace this if it becomes damaged. This would have to be inspected by a qualified person to determine if the platform step could be replaced.'
Sounds like, if you are unsure, then it may be worth replacing them.