But the thing is, your lens is fine before sending in to CSC.
No parts to replace is not an excuse.
They broke your lens, its only right for them to replace one for you.
Your lens is 5 years old, so what? This lens may last you another 5 years.
In any case they damage your lens, the compensation is inevitable, if the resultant loss of income, you can also ask them for compensation. (Lens no 10 year COE, 5 year is still young)