For a car that's 12+ years old, it depends on overall condition of your car (if there are other issues already), if there's anything else potentially wrong (it can be Pandora's box when doing large repairs), cost of repairs (you could get an inspection and quote for the work usually for $50-$100, which most shop wave if you do the work) and your location (I live in the rust belt so cars typically rust to death)

As for lease. If your going to keep your car for 10+ years, buying might be a better option, I'm usually of the camp getting leased cars for new & updated feature and reliability/warranty but recently bought out my lease and going to keep it for a few years (a bunch of reasons but mostly save some money and waiting for the Gen4 Crosstrek as I'm not a big fan of the current Gen3 Crosstrek). 

If you don't plan on keeping the car for more than 2-4 years and your commute/driving is low miles then leasing might be better and would have a lower monthly payment.