[Richard_FM]

I've heard of some of the early colour video tapes of Doctor Who returned from Canada in the 1980s were shedding oxide, & had to be carefully transferred & converted back to PAL as the returns were NTSC conversions.

I'm guessing these tapes would have been made in the mid 1970s, around the time of the whale oil ban, & used a formulation that only lasted a few years before deteriorating.