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Sounds ominous re: oil pressure light.
Haynes manual recommeds jacking up car to gain better access and removing right hand front wheel plus undertray followed by wheel arch liner itself. The switch itself simply unscrews out and a small amount of oil spillage is normal. Recover the seal and when refitting a new seal is recommended. Clean-up and refit then top up oil as necessary.
Also worth checking and if necessary replace the oil filter just underneath the pressure switch. Remove sump plug, drain oil, clean and refit using new filter. If for some reason the sump plug or filter is damaged or installed incorrectly this is where you could be losing oil from too.
If your car has air-con then the oil cooler is in a similar location and so it's worth checking around that for oil leaks.