sporty coolent temp


hi i have a 1993 sporty and it kept on cutting out and was a pig to start again i crossed the pins in the engine management plug under the bonet and counted the flashes and it came up with coolent temp sensor i got a new one and came to swap it and i couldnt get it out as it has siezed has anyone had this problem and what are the chances of it breaking off in the head.
Any help will be greatly recevied many thanks jon