The honest limitation: if the door panel is delaminating or the wood core is rotted through - common on original 1960s wood doors that have taken 50 winters of freeze-thaw - no spring or roller swap fixes that, and we'll say so rather than patch around it.
Another complication is parts lead time on older hardware. Some bracket sizes and wind specs from 1960s-era doors aren't something every supplier carries on the shelf, so a repair that would take an hour on a newer door can mean an extra day waiting on a part for a Bridgeport house. We'd rather tell you that up front than promise same-day on something we can't source that fast.
Last, because there's no local branch here, every visit adds the drive from Saginaw into scheduling. It doesn't change the price or the work, but it's part of why we ask for a little flexibility on timing rather than a fixed same-day window.