@andreavic it will be helpful if you can post some pictures with your question of where exactly the damage is. Use this guide [guide|21499|commentid=417084] for that so we can see what you see.
Your alkaline battery is most likely leaking and it is absolutely possible that one of your batteries has ruptured. You need to remove the batteries. Then clean everything with a fine brush first (wear some eye protection against any flying particles) and after that use a cotton tip applicator and some vinegar to clean the corrosion off. Then evaluate all the contacts to make sure they are still complete etc.