2002 Acura RSX Engine oil leak

Had car in for service (an independent I have used for some time). Mechanic told me that there was evidence of an engine oil leak. He said it could be addressed initially by switching to a heavier oil but, ultimately, the cost to repair would be $1,800. He did not give me any specifics about the leak other than it involved the engine.
The car has been serviced regularly, is housed under a carport in Tucson (hot) Arizona. I am having difficulty understanding why, despite its age, a car with relatively low mileage, driven by a conservative driver, could develop this costly a repair.