Ian wrote: 74 series logic from Ebay can be a real problem. :-/
That's a general problem with older parts. There seem to be quite a lot of Chinese product counterfeits around, especially when it comes to obsolete parts. I avoid buying those on eBay, especially when they are shipped from China, but even with local distributors/dealers you may be out of luck. Some time ago the PSU of my Harman Kardon speakers for my Mac died due to an overvoltage event and killed the audio amplifier of my SoundSticks subwoofer. It was a TDA8510J - a part which is out of production for years. After some research I found a distributor who claimed to have NOS of these, in fact none of them was working, all with different types of failures which in one case nearly killed my woofer.
Finally I found an automotive version (the last IC remaining of the whole family) which I could get from one of the renowned distributors (it was DigiKey or Mouser), the model was not fully compatible but easy enough to adapt (just one inverted output) et voilà, finally the speakers worked again.
BTW, regarding the 74141, ti is linking to Rochester Electronics, who have licenses to manufacture these parts, but they will cost you an arm and a leg.