Dave s no I am a field service engineer and ye s depending on how big the ram was and if there was some thing or some one to help lift it out there is no reason it cannot be done on site.
However a lot of companys these days will not allow that sort of work to be under taken on site given that they are also responsible for your health and safety.
In days of old there isn`t a job that could not be done on site and yes I have done just about all of them at one time or another.