[Crono]

Hi! I've got what's becoming a pretty high mileage '92 Metro (around 300,000 miles / 450,000 km) and I've been trying to catch up on some neglected maintenance. (For a while I was just doing the minimum because of money considerations). I'm wondering if there are things that I should be looking at in particular that might go wonky with really high mileage, like sensors, fuel injectors, filters I might not know about, particularly that will affect fuel economy. (I'm pretty sure my O2 sensor needs replacing for one, as I'm getting engine noise under load, particularly uphill). If I'm looking at replacing some sensors, are there any aftermarket options that are superior in terms of fuel economy?

Any thoughts or suggestions would be appreciated!

PS I already do my regular maintenance like spark plugs, oil changes, air filter, etc.