Keep in mind that 'damage' causing leakage can be anything from a deep scratch to a slight bend. One the hard chrome on the piston rod (which is what you refer to as the 'silver arm' which is really the piston rod si compromised, the seals will weep. Why, instead of attempting to replace the seals, it would behoove you to take it to a competent hydraulic shop and let them inspect and repair it. Not gonna be all that expensive in the first place and if they do it, you have a guarantee that it will be right. If you do it, there is no guarantee at all and if it still leaks, it's 100% on you.