One of the most common problems with pianos in Cape Town and Durban is the swelling of the lead weights inside the keys. The lead oxidizes and expands causing problems with keys which get stuck. This can be rectified by removing all the keys, removing the excess lead , then painting the weights with lacquer in order to prevent re-occurance. This procedure can take a good few hours if done properly and should cost about 1½ times the price of a tuning. If however the expansion has been allowed to progress for some time it may have caused a splitting of the keys and in which case the weights must be removed to allow the keys to be repaired. The weights may also need to be replaced. This scenario would involve a a significant extra cost depending on the extent of the damage.
I have noticed this problem in at least 25 % of the pianos in my care and enclose a photo of a note recently found in a Steinway Grand which I was servicing.