Yesterday, in a flash of illumination (literally) the sun hit the front
door and around the lip with the rubber seal I noticed I could see
daylight in places. This explains at least one of the draughts I've been
trying to track down (it's an old house). I can usually manage to stop
draughts with one or more of an array of 'stuff' but I'm not sure how to
resolve this one, the rubber strip looks OK, should I look at replacing
it or is there something else I should be looking at?

Before anyone mentions it, the company who installed is long gone so
there's little to no chance of recourse there and even if there was, it
wouldn't make my house warmer quickly.
--
Clint Sharp