The most common surprise on a Manchester roller call is finding the track itself pitted or slightly rusted where a worn roller has been grinding metal-on-metal for months. Our climate here runs mild with occasional freeze rather than hard winters, so it's not ice cracking the rollers - it's just age and friction wearing a track that's been in place since the house was built in the mid-80s.
The second thing that turns a simple job into a longer one: a bent bracket. If a roller seized and got dragged sideways before anyone noticed, the bracket holding it can bend just enough that a new roller won't sit straight until the bracket's replaced too. That's a five-minute fix once we're already there, but it's not something we can price sight unseen.
Last one - doors with a spring that's also near the end of its life. Rollers can fail years before a spring does, but on a door this old, if the spring lets go mid-job that's an added repair, not a roller problem, and we'll walk you through that separately if it comes up.