The problem with the Hartal locks is not normally associated with the barrel. The problem is with the inner grey part where the shaft through the centre attached to the handle becomes almost seized in the housing.
We normally remove the circlip to release the handle and then run a slightly larger drill through the hole to give a little more clearance where the handle rotates.
With regard to the barrel itself we have had little success in removing the barrel from the outer casing which contains the grooves. You will probably need to buy a complete lock assembly if you are having problems with the barrel.