How old is it and is the ground water high? They do rust out in wet areas. See if it works OK first. They usually will jump erratically if they have a leak and the oil gets low.
I saw one get dug out years ago. Jackhammer at least 2 feet around if not more to loosen the soil around it as deep as you can. Then these guys unbolted the "lift head" and then used a backhoe to shake the cylinder from side-to-side for quite a while while pulling up.
I don't recall where the buried air pipe was located though
I will be looking for one next summer...I'm going to contact a guy who ran a business that remodeled gas stations and I'll bet he still has contacts for getting me one. I do mostly bodywork and I can't use a side-post lift.