After taking some very good advice from the professional toobers on here I did the following on a PVC repair which involved removing the old glue.
1. I Heated the workshop up with a gas fired blower. This makes the PVC much more workable.
2. I Used MEK Solvent (Butanone) and much elbow grease to remove the old glue and clean the tube surface. It did not discolour the PVC.
3. You must remember to use Chem Barrier gloves as the MEK will eat away the latex disposables.
4. You must turn the gas blower off before you start with the MEK or you might have a nasty fire.
5. You must use a well ventilated area and face masks etc as it is pretty nasty stuff to use.
If in doubt ask the guys in the trade on here and they will give you excellent help and advice.
After 8 years that clean and repair job is still as good as the day I did the job. Good luck.