These engines go into a death spiral once the valve seals become hardened by heat at about 100,000 miles. Oil leaks into the combustion chamber & sticks the rings, causing even more oil to blowby. Then carbon deposits onto the exhaust valves and they burn, causing the affected cylinder to stop firing. Your EGR channels will also be totally clogged with soot.
THE ENGINE IS NOT WORN OUT. IF YOU DO NOT HAVE BURNED VALVES, you may be able to (best case) replace the valve seals (perhaps even without removing the head) and unstick the rings with some kind of additive.
I had burned valves in mine – but the original honing was still visible on the cylinders with no detectable ridge. I replaced the exhaust valves, valve seals, rings, main and cam seals, and now at 170,000 miles I get the usual Metro mileage (about 45 mpg) and the oil stays clean for 2K miles.
Persevere – these are great little cars and should run a LONG time if you know the tricks.