Just replaced my left rear brake caliper, locking up again, is it caliper or distribution ? any input appreciatied

 

try cracking the the steel line at the flex hose check to see if caliper still stuck then crack flex hose at caliper if caliper releases replace flex hose

 

You say you've just replaced it and its locking up. Sounds like the overhauled unit hasn't had the inner seal replaced and piston.
Either take it back and tell them the fault or strip it down yourself and clean it out yourself then rebuild. Course you should find it clean inside.
If not clean inside you have recourse. If clean, rebuild it with preferably new seal (seal must be at fault).
Its all roundabouts here and coming back to faulty Calipher..
Good Luck.