74 vs 47? Just goes to show: the printers themselves are just a cheap (but effective) wallet-opening devices, from which will flow hundreds if not thousands of dollars/pounds in ink purchases...

Another update. I have found a superb forum here:
Clogged Canon print head | PrinterKnowledge
It was started five years ago and is still going strong. The amount of DIY expertise and information with regard to cleaning and maintenance of inkjet heads on this forum is quite staggering. I was curious to discover whether it was possible to strip down a printer head to see where the problem might be. The answer is yes, provided you have some DIY or engineering knowledge or both. However, there is a lot of advice there regarding removing blockages before getting to the strip-down stage. I am minded to buy the MG3250 anyway, change the head over and then work on the old head. Watch this space.

A little bit more on this subject about inks. I was explaining to my youngest son, who is an archaeologist, about my printer problem, and he pointed out that cheap inks do not provide long-term stability for hard-copy photographs. Canon inks are guaranteed to be stable and provide archive quality for up to one hundred years. This is important if, like us, you are producing hard copy photos for your family to keep and pass on down through the family archive. So what I intend to do is to purchase the MG5250 and. once installed and running, repair the head of my existing MG5350 and then fit one with Canon inks for archive photos and the other with cheap inks for day-to-day stuff. Incidentally, after the last clean, the 5350 has worked perfectly.