I am pretty sure my breakaway switch was original to my trailer - so 13 years old.
It was a Tekonsha model 2010. A brand new switch (the exact same model) is only $9 shipped from Amazon, so I decided to replace it.
When I removed the old switch, I found the interior to be almost completely rusted out. It felt like it was full of sand from all the loose metal inside. While it did pass a continuity test on my circuit tester after I pulled the pin, I have no confidence that it wouldn't have melted and failed with significant current passing through in a real emergency.
You can get an idea of how rusty the inside of the switch was from the picture below. Note that it looked fine on the outside.
I definitely did not expect this to be an item that would wear out - so just a heads up that they should be inspected and replaced periodically.
Even with soldering and heat shrink tubing the leads for the new switch (improving on the old wire nuts and electrical tape from the factory) - te total time to install was less than 10 minutes.
Here is a link to a new switch on amazon - Tekonsha 2010-P Nylon Breakaway Switch with Weldable Tab : Amazon.com : Automotive