How long should shocks last on a 1992 300D ?

[kamil]

Just out of curiosity I'm wondering as to how long the shocks can go for before they are changed. My dad said that when he goes over bumps he hears some type of gas coming from the front wheel well. I just figured that it was a shock that's not performing well. I believe that they are still original so that would make them 12 years old and 125,000 miles. Any ideas ?

Thank You