I've taken the heater out to refurb it and the lower screen seal has rotted away. My question is......do I have to undo the screen jacks to fit a new lower seal? Will the screen stay in place while I do this? Anything I ought to know before I tackle this job? Luckily I've caught this before before any real rot has set in under the heater as a previous keeper had stuck the scuttle to the screen with copious amounts of mastic!