WOW Baz you have certainly got a load of mess.
(a) Nope, as above, self-cancel is not relevant to MOT. It can be annoying and dangerous but, as the driver, you are responsible for ensuring indications are correct - i.e. manual cancellation in this case. I agree with woofgang, sharpness of turn is the test (and it varies from car to car); (b) for MOT failure list, refer to last MOT certificate and the mechanic's recommendations for future attention. Mind you they've changed the certificate again this year!; (c) Aagh, the agony of all motorists: this bloody computerised display. I heard of someone re: airbag light always on - he has ignored it for years, withour probs, and is still alive - however I cannot recommend ignoral; (d) READ THIS!
I THINK YOU ARE WORRYING ABOUT SMALL-BEER as your major problem seems to be the oil-leak/cam-belt. Sounds like the head-gasket is blown. Expensive. But even more critical is the cam-belt system, if it's not right. If YOU link the oil-leak to cam-belt change [I bow to experts here] but speaking as a car-mechanic-innocent and fellow past-sufferer, it sounds like timing of the belt is wrong or there is a failure in the timing cogs or the plastic runners (the kit).
It is NOT sufficient just to exchange the belt, as though it was the cooling belt, but to have the WHOLE kit checked, possibly renewed and then the correct timing set. The cam-belt, formerly the "timing-chain", and the whole kit is VITAL! If this system fails then the fuel valves will be bent and that means a "new" car. Even worse, failure could bring the car to a sudden stop. The latter is deadly if you are being tail-gated (illegal but idiots still do it).
If it's out of warranty, DON'T put it into Dealer's-hands (in your case Peugot). Find a good "sole-trader" mechanic who knows his stuff. He might even say "dump it, not worth throwing more good money after bad". Peugot or Other-Make Dealers will never say that! Sorry for pessimism and hope others wiser than me are more positive.
Good luck Baz.