Depends whats in it but if its just scale then a citric acid solution would do the job. Dissolve some Citric Acid in hot water at a ratio of 1g to 100ml of final solution and add it to however much cold you need to make it up. E.g. to make 1L, dissolve 10ml in hot water and add it to ::) 990ml of cold water. Rubbery figures of course, something along those lines will do.
I wouldnt use silicon for the seals; just get new ones is the best way if theyre available.