Think about it this way. Suppose the timing chain and rails last until 200,000 miles. What is a decent 400E with 200K-miles on it worth? Suppose that number is $5000.
You could invest $1000 to prop up the salvage value of your asset to $5000. If you don't, and let the engine break, a 400E with a broken engine is worthless.
If you are at the point where you don't want to put any more money into the car, then I would sell it and buy something with lower operating costs.
All IMHO, of course...
1998 C230 "Black Betty"