Hi,
Please advice, I need the XK Gearbox O-ring seal part number for the O-ring shown on the attached picture with the arrow.
Or dimensions please, it looks flatter than O-ring, so might be other shape than O.
The O-ring was not included to the gasket set supplied by the UK XK specialist supplier.
Your tailcase casting is not for an XK120. It appears to be for a Mark VII.
The serial number will be a JL or SL but there is no rear mounting on it.
In any case, Jason is correct that the part number of the o-ring is C.4284 and an ordinary rubber o-ring should work. Your old one is distorted from age and being confined in there.