Don't have a manual box .. buta quick read of "the Book of Lies" shows a "procedure" for adjusting the gearbox linkage ...
"Note: Vauxhall service tool KM-631A will be required to carry out this procedure.
1 Adjustment of the gearchange linkage is not a routine operation and should only be needed if the mechanism has been removed. If the gearchange action is stiff or imprecise, check that it is correctly adjusted as follows. 2 Position the gearchange lever in the neutral position, firmly apply the handbrake then jack up the front of the vehicle and support it on axle stands. 3 Remove the retaining clips securing the protective cover to the vehicle underbody then fold the cover forwards to gain access to the clamp bolt on the rear end of the gearchange linkage rod. Slacken the clamp bolt so that the end fitting is free to move easily in the rod (see illustrations). 4 From inside the vehicle, unclip the gearchange lever gaiter from the centre console and fold it back over the lever. Free the rubber gaiter from the mounting plate and fold it back to gain access to the base of the gearchange lever. 5 Lock the gearchange lever in position by fitting the service tool (KM-631A) into the gearchange lever housing whilst holding the lever over to the right.
3.3a
Release the retaining clips (arrowed) . . .
3.3b
. . . and peel back the protective cover .
6 From underneath the vehicle, using an open-ended spanner on the flats provided, turn the gearchange linkage rod fully clockwise (as viewed from the rear of the vehicle). Hold the rod in this position then tighten the rod clamp bolt first to the specified stage 1 torque and then through the specified stage 2 angle. 7 Remove the service tool and check the operation of the gearchange lever before seating the rubber gaiter onto its mounting and clipping the gaiter back into the centre console. 8 Ensure the protective cover is correctly seated on the base of the gearchange lever, securing it in position with the retaining clips, then lower the vehicle to the ground"
There is a further procedure for removal/refitting the linkage ..
Haynes Ch 7A.3 & Ch 7A.4
HTH