Grovel, grovel, scrape, scrape! I have to apologise to you, Squashy, for my over-hasty earlier response! I made the mistake of looking only at the listed word, 'sez' and just took my own (Scottish-educated!) pronunciation into account. Although resident outside Scotland for over half a century, there is obviously still more than a tinge of the old Jockanese in there!
Fred, as you say, The Oxford English Dictionary gives 's+backwards3+z' as the pronunciation of 'says' which its sound-table suggests is the 'e' sound in 'pet'. So, you're right that it means 'says' is now pronounced 'sez'.
Accordingly, you're right and I'm wrong. However, I'm sure I shall continue pronouncing 'says' just as 'say' with a 'z' tacked on and not as 'se' with a 'z' tacked on! Must listen more closely than usual next time I hear HM speaking. (Mind you, she says 'nace hice' for 'nice house', so I'm not sure we should treat her as a role model.)
Again, my apologies, Squashy.