Ive actually got a copy of what I was told was the last Chieftain manual issued, and it says the engine was the Mk13A. Im not saying there was no higher versions of that, but Im not sure by that point there was any development room left in it. I think they must have started fitting that in the Early 1980's, and as one British author noted 'Though the Tank is the Mk5, the engine is the Mk13, and many would still say its a long way from perfect'. Which is presumably why they trial fitted an MTU engine in one of them.
The odd thing is, when you talk to some of the people who operated them, you get a much more mixed picture of the reliablity. Bob Griffin (who used to post here as Commander) was a Chieftain crewman and gunnery instructor, and crewed a Mk2, which should in theory have been the most unreliable version operated. In actual fact he claimed his rarely broke down, largely because he followed the maintenance schedule. The suspciion is in cash strapped and overworked BAOR, not everyone did.
Re Centurion, from what I was reading last night we seem to have been supplying ammunition and spares to Israel still in 1973, when we called it off due to the Egyptian blockage. I was quite surprised, I thought we had cut all ties in 1967. So Yes, that they still had British ammunition I guess should be no surprise.
We keep going on about what a bonanza the 1973 war was for studying Soviet kit. Seems the reverse as also true, and the Soviets had a real haul when the Bar Lev line as overrun.