I resealed a main lift ram on a triplex mast only a couple of weeks back.
If there is suitable working space then it could easily be done on a site.
I do know some customers don't like any mess being made & also some customer's wont allow any mast / ram removal's on there sites so in those cases the machine would have to be uplifted back to the repair centre.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.