A good used Moss Gearbox speed change housing, Jaguar part number C14468 it came off a MK2 gearbox but I think it fits a number of other models including the early S1 E types 420's and S Types but obviously check the part number is compatible with yours before committing to purchase.

Just to note there were two types of these speed change housings, one with the breather located in the side and one type where the breather was fitted to the gearbox lid. This one is the type where the breather was fitted to the housing not lid. both had the same part number though. 

You will need a new 'O' ring part number C12454 which you can get from Barratts for about £1

It's in good used condition and might be of use as a spare or if yours is damaged.