You have to wonder what causes a sudden spate of failure in these after 40 or so years of solid service. Generally, ICs are highly reliable unless subjected to external causes of failure (improper power supply, inputs out of safe range, ESD, harsh environment). I have multiple receivers and tuners using this chip and all have remained reliable thus far. Of course, I probably just smoked a chip posting that.
Then again, we are coming to find a lot of small signal transistors, which had long been thought to be nearly failure proof - if operated within spec - are simply going bad (typically going noisy) from age/environment. This is probably somehow related to less than ideal manufacturing, leading to an eventual breakdown even if kept within proper specifications. So much for solid state I guess.
This doesn't bode well for the future of a lot of vintage gear, as many parts are already "inobtanium" now or soon will be, and do not/will not have suitable substitutes, at least not without a lot of reverse engineering and effort as with the MSM5540. Most concerning for late 70's gear and onward that more heavily utilized specialty IC's and other application specific parts - chips most notably - that were once ubiquitous but are long since obsolete decades on.
We are presently getting a small window of opportunity for some of these parts which apparently were socked away for many years in warehouses around Asia, and for various reasons (ebay, Alibaba, internet semiconductor search sites and renewed interest in these old parts literally creating a market again) the infrastructure now exists for these wholesalers to get these chips sold to parties looking for them. This won't last indefinitely, as the stockpiles of these parts are not that deep to begin with in most cases.
- we need solved cases like this to build up a knowledge base for these digital display issues. 