my cousin just gave me her car but it got a blown head gasket and there water in the engine. the oil on the dipstick looks like chocolate and when i open the oil cap i can hear the pistons slushing around a the sludge that's in the engine. i don't know how to change the head gasket and i probably wouldn't trust myself in changing it. should i hire someone to change it? is it even worth investing money to change it? the engine only has 100,xxx miles on it so it figure its still good? what would you guys recommend?