(1971, dir Chuck Wein)

A kind-of documentary about Jimi Hendrix features over two minutes of footage of a bus being driven from Hollywood to San Diego with a woman on board. (thanks Simon)
In summer 1970, a New York Model (Pat Hartley) travels to Hawai'i, to an outdoor Jimi Hendrix gig near Olinda, southeast of Makawao, on the northwest upcountry slope of Haleakalā, the East Maui Volcano. It's actually the last Hendrix gig filmed. While in California she's given a sightseeing tour on a 'London Transport' bus.
Prior to that we briefly see this GM 'Old Look' parked:

The 'London' bus in question is a lowbridge AEC Regent III/Weyman, and bears fleet number RLH78 (there were only 76 London Transport RLHs). However its history is interesting: in 1950 Midland General ordered thirty AEC Regent IIIs with Weymann lowbridge bodies, but in the event only ten were delivered. The balance went to London Transport as the first batch of RLH-class buses. The ten for Midland General were ONU630-9; this is ONU632, which was given this fake fleet number before export to California. More information can be found at the RLH Bus Info Centre

They pass a Flxible 'New Look':

She rides the platform, she also rides upstairs. It's unusual to see the lowbridge layout upstairs:

Eventually the driver pulls over to inspect the engine:

Less exciting at the airport is this US Army bus with a GM 'Fishbowl' parked behind:


Incidentally a documentary about the filming of the gig, titled 'Music, Money, Madness…Jimi Hendrix in Maui' describes the film makers gathering up people to go to the gig on a hired bus. No external view of said bus, but we see a few seconds inside of what appears to be an RT family bus: