This is what is given in the start of the Haynes Manual Mark if it helps
.
Manual transmission:
Early (pre 1999) vehicles:
Up to number JP3097A01361659
* . . . . . . . . . . . . . . . . . . . Vauxhall transmission oil 19 40 704
From number JP3097A01361659
* . . . . . . . . . . . . . . . . . . . Vauxhall transmission oil 19 40 764
Later (1999 onwards) vehicles . . . . . . . . . . . . . . . . . . . . . . . . Vauxhall transmission oil 19 40 768
*The identification number is stamped on the transmission housing. Note: There have been three different types of oil used in the
transmission by Vauxhall. The different types of oil should never be mixed, and it is essential that the transmission is refilled either
with the same type of oil as that drained, or the latest oil used in production from 1999 model year. If it is not known what type of
oil has been drained, the transmission unit should be flushed before filling with the latest specification oil. To do this, refer to
Chapter 7A, Section 2.