It is got 145K miles. Owned it for the last 3 yrs. Loved it. But engine starts to leak oil. Dealer wants $1300 to fix leaking gasket.Is oil leak stopper fluid additive gonna do damage ? Maintained the car religiously.

Whoa! 1300 for a gasket! l would let it leak and just fill it up daily. l would ask exactly where the oil is leaking from. If its just the pan then do it yourself for 50 bucks. Otherwise, the question becomes whats the car worth to you? its 11 years old and high mileage, l would put the money away and start preparing for a new car.

where is the leak coming from? the front crank seal/ oil pump seal?

Why would you EVER take that car to the dealer?
They are ripping your lips off. Your front crank seal is leaking.possibly your cam seals. This should cost around $300 just about anywhere.

Simple solution, find a different mechanic.

Do NOT add any stop leak! You will mess up your oil pump in time.

Get the gaskets changed its common on those cars for that year. Maintain it and it should last another 60-100k miles. Make sure if you do shop around for the work the mechanic kows what he is doing.