Symptomatic of low ATF. First thing would be to check ATF level and ideally a fluid & filter change.

As RobG says. There is a guide for checking the level properly  in the Maintenance guides. Auto Gearbox oil should be changed every approx 70,000 miles - more frequently if towing a lot. It gets overlooked and there isn't a drain plug. Again if it needs doing there is a maintenance guide for that as well.

i tryed to order new filter from vauxhall and was told they dont do them anymore. discontinued product.

Or just wash the old filter out.

many thanks for the replies, now i'm wondering whats best and easiest,stripping out and fitting new filter or fitting second hand box my car is 2.2 petrol cd auto 2000.i live 23 miles west of glasgow what kind of delivery cost are we talking.

All you need to do is remove the sump from the bottom of the gearbox then replace the filters and fill up with fluid once its back on...worth doing first as worst case scenario you could re-use the filters and probably most of the fluid and you would more than likely need to change both on the replacement second hand box anyway...

Courier of a gearbox on a pallet to Glasgow will of course to a degree depend on distance...from here probably about £50-60...

Its an easy enough job even for a beginner, just bear in mind that it will be very messy when you remove the sump...have something if not a lot of something underneath the gearbox sump ready for when you have removed it...and try not to get a lot of it on you...old gearbox oil is very messy and STINKS! And the smell stays around for weeks...wear really old clothes and chuck them if it gets on them...gets in your washing mahing too otherwise...I really cannot stress this enough lol