I don't know how this myth that part timers had no say got started but it's wrong. Make your request, make it known to your BA, then file a grievance when the contracts violated.
Article 22 section 4
Part-time employees with six (6) months or more seniority shall
have the right to place their name on the list of employees waiting
to be moved to a preferred job within their building. Such preferred
jobs shall include, but not be limited to: Preload, Sorter, Clerical,
Irregular Train, Designated Responder, Carwasher, Loader and
Unloader. Employees do not have the right to select any specific
unit, load or workstation unless a prior past practice has been estab-
lished.