It all depends on the type of pump. There are rebuild kits available for the Par pumps, I am unsure regarding the sureflo models. Unless you are trying to keep it all original you may be as well off to get a new pump as to try to find a repair part. It all comes down to a matter of time and money. It sounds like your trailer might not have been properly winterized
You may be chasing leaks of a while. Good luck.