Improving the gear shift?
I guess you mean the auto shift lever, as most 463s in the UK were autos?
If so, you will need to get underneath with an oil can and lubricate the links. The pivot mechanism under the level, but inside the car should also receive a drop of oil,
If you are referring to a manual transmission, then have you tried changing the oil?
I'm guessing it's a manual?
If it is manual, get some spray grease etc, get underneath with a torch and you will see the bottom of the gear linkage near the central propshaft, some metal bushes/washers get rusty in there, douse in oil and will be much improved, tho unfortunately I think there are some plastic parts in there as well which oil will not prolong life, but probably worn anyway. Mine suffers after use in snow.