Sorry a little miscommunication there :-(

I thought you were referring to the winch that pulls the boat onto the trailer.

Regardless, you should be able to spray a non-grease lubricant on the jack when it's fully extended. Then just work it in and out of the housing a few times.

A zirk fitting is the little fitting in the picture in the middle of the 'X' just below the socket. If you have a zirk fitting, just take the trailer to any tire shop and ask them to pump a couple squirts of grease in there. They shouldn't even charge you.

http://www.calfishing.com/dc/user_files/3231.jpg