I have a mk7 overdrive that is leaking oil quite badly from both sides of the cross shaft from the solenoid,Am I right in believing that there is a square shaped cross section o ring externally either side ? if not could someone point me in the direction of the cause of this
This is from the Mark VIII parts catalogue. It sounds like you are referring to Item 8 here.
It is an o-ring, no other description, but Jaguar part C.10378 or Laycock DeNormanville part 64486.
Triumphs and Volvos also used this OD so that may be an easier source of parts.
Looking at the Plate XX, I think it is likely that the o-rings are square cross section and inch sized rather than metric. In that case, a source I have used is www.mcmaster.com for square section o-rings, but you’ll have to measure the pocket and figure out the correct size.
Thanks for that information really helpful