X10 has always changed components inside modules and, in some cases, changed the boards significantly without changing part numbers. I don't understand this practice, but that's kind of their thing. I can't say that a module would degrade over time as I'm not a hardware designer, but I can say that over time, some components do deteriorate. For instance, many capacitors degrade with or without use to the point where they can destroy the device. I don't know if that could happen with these modules but it's something to consider.
That said, I agree with toasterking that these motion sensors are terrible. I have used a number over the years and have concluded they are not worth the effort. The range is terrible even after adding a passive antenna. They die without any warning (many devices send a battery low indication, these just stop transmitting). When they die, it's usually around when the batter has already been leaking for a few weeks or longer so the module is already damaged. And they are for "indoor/outdoor use" which means they should be able to survive basic use outdoor instead of having to be sealed for even occasional light rain and even then fail because the components can't be exposed to UV without cracking.
Some X10 is pretty good. MS16A is not one of them IMO.