Help with a busted MSV11-L?

So, I seem to have discovered a plague! I had another failed QBUS memory card, an MSV11-D this time (M8044-DB). It has the exact identical symptom, except with a different bit - 02000 this time, instead of 020. So, since the designs are very similar, I thought 'maybe another bad S373'. Well, they aren't quite as similar as it thought, but the culprit is indeed apparently ... a bad S373! (Although I have to caveat that; I suppose it could be the bus transceiver it's connected to.. but the output is always high, which make it seem like the the driver in the 'S373 has failed.) Anyway, this time it's a National Semiconductor part, and from a very different date code (7947). What is it with S373's? Is this just pure chance, that two from different makers, quite a while apart in time, were the culprit? Or is there some issue with S373's? (I note that MSV11-D's are apparently notorious for failing; perhaps because they use S373's a lot?) I do have another MSV11-D with a similar fault (the 01 bit this time); once I get it fault-isolated, I'll report if it, too, is caused by an S373 failure. It may take a while to get it fault-isolated, though - so far, I've been writing two- or three- instruction loops which have the picked bit set in all the words of the program! (Because I'm too lazy to write a longer program that sets up the memory mapping so the program can run out of 'good' memory, only poking the 'bad' memory to test it... :-) Also, it's kind of an fun challenge... :-) Noel