Lately I've been using use automatic transmission fluid; got a liter-size bottle for free, so why not ttry it? Its slightly 'thin' by oil standards (seem like 20W motor oil), so probably works well penetrating the links/rivets. So far no problems.

You might also try some of the motorcycle chain lubes, which you can usually find at general auto parts stores. There are some blended specially for winter or summer, so they would probably be good for a bicycle in either season, too. Also types available that won't 'throw' off a revolving chain, but they're sticky and will collect dirt quickly. None are as expensive as specialty bicycle lubes, even if bought at a motorcycle dealer instead of an auto parts store.