Coolant leaking into the engine?

Car has been driving very well since timing belt change a month ago. I went for service and the garage noticed it was running low on coolant. They eventually found that coolant was leaking into the engine. They seem to be sure that the engine needs replacing but all the research I have done suggests it requires stripping and replacement of any damaged parts. As mentioned, it is running fine, has not overheated and the temperature seems normal when running. Please help. Thanks, Steve Burgess