Shaft Reg

vauhxall astra 1.6 8v manual petrol Y reg. problem in shifting gears.?

car has only done 30,000 miles and got it serviced last week. im having problems with shifting gears. dealership did had a look at clutch and they reckon its fine and got the gear shaft lubricated. but while driving when car gets warm its really hard to shift gears from 1 to 2nd and so on. gear stick feels rock solid and when i put it on reverse it makes cramping noise. the problem is not continuous but do happens when i am driving for longer period of time. any ideas please? could it be gear linkage or gear box?

Believe in lost of fluid pressure on clutch master or sub cylinder.
It may not be leaking out but internally in-between rubbers.
at 30,000 miles,doubt on a faulty pressure plate or gear box.