Seized in the CDL functioning position, or seized in the CDL off position.?
The former is far more of a problem than the latter.
I take it you have tried holding the lever to the right and reversing and driving forward again to release it?
If not a bit of jacking up axles, twiddling wheels and gentle tapping with an ammer to try and free it off? (Would take two peeps I'd imagine.) As it lives in an oily and otherwise clean environment, as opposed to the linkage, i'm a bit surprised at this.
Or did someone try and do summat daft with it engaged which might have led to overheating then seizure?
As much info as poss will help.