Hey Leo, as it turns out the pins on the Canon 5D (original) some 15 years plus old has pins that a minutely larger than the newer Canon 6D11.
So if i press really hard and I mean very hard i can get it on the 5D and it triggers, but getting it off is extremely hard and need to be levered off gently, which works but is a scary process
and wondering if the pins are going to come out with the cable.
Anyway I have found the answer, and as you said maybe the smallest amount of WD-40 might help.
Thanks for your suggestions.
Leon
