Show the points where movement catches as well as the full track. Local damage may have a different repair option from extensive wear. Photographs help describe the problem but cannot establish that the track, rather than the rollers or frame, is the only cause.
Loose or damaged fixings can affect the running surface. Accessible fixing points need sound support for ordinary work to proceed. Deterioration beneath the rail may require a different assessment; covering it with a new section does not restore an unsound base.
The extent of wear, available parts and access affect the choice. A small repair may be reasonable on an otherwise sound compatible rail. If replacement requires specialist panel handling or rebuilding the threshold, it falls beyond the ordinary task offered here.
Repair an accepted accessible rail or fit a compatible running insert or replacement section without changing the building envelope. Scope limits: Accessible non-structural running rails only. No threshold waterproofing alterations, drainage-system redesign, structural changes, major glazing or powered operators.