The chain could last until 150K, but look at all the exposed guides, as they do get brittle and cause the chain to pop when they break.
Search the archives for directions on checking the timing chain stretch and have it changed if it has stretched too much.
When you have it done, consider replacing the plastic bits of the cam-oilers, too. You can get this done for closer to $600. Cheers, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo