A good used Laycock overdrive accumulator piston as fitted to quite a few overdrives in the Jaguar range, it was probably fitted to many other British classics fitted with Laycock overdrives to but obviously check compatibility before committing to purchase.

Item 45 in the illustration and part number 8030 or I think the Laycock number is 65664

there are some marks in the outer surface where the piston has been operating but this item still has many more good years of service left in it.

Comes with the original piston rings ring but it might be worth replacing these for a new ones.