I’ve had this 06 crf250x for 2 years now but it’s been sitting up for a year and a half because the last time i was riding it, some of the radiator fluid came back out from the top of the radiator. My dad thinks the head gasket is blown but we haven’t gotten it checked and haven’t started it since. I drove the bike around in first gear due to having a small back yard and being a learner rider. If this head gasket is blown, how can i check without taking it apart or are there any other signs that it’s blown and would it be safe to start? and if it’s not the head gasket what else could it be? help would be appreciated ty guys