Not only on service 980...
Service 857 also have a loss of bendy buses on Sundays/Public
Holidays (from full fleet to only 3/4 bendies) 
Service 960 also used to have full bendies too, nowadays tend to
see a few rigids on service 960.
I think that some of the WL controlled services (like 856, 912, 913
etc) switched to perm rigid deployments on Sundays/Public Holidays
apart from full bendies on weekdays/Saturdays 