Does anyone know if the TJ tensioner is a sealed unit or does it get oil/pressure from the oil system of the car (i.e. oil pump). If it is pressurised by the oil system, is there a seal / o-ring??? I am gearing up to this #$@% job. Should I replace the tensioner? If one pushes on the belt it goes slack, then if you run the motor and check it is tensioned and once again by pushing on the belt one can induce slack........So I assume it is tensioned by oil pressure from the oil pump or when the belt pushes against the tensioner it's internal pressure responds. I am accustomed to the system on the TS v6 where the tension is static, that is the spring applies tension and after that one tightens the nut to secure the tensioner pulley.

Sealed unit. Does not touch the engine oil.

Yep, sealed unit. Cost mum about $400 when it let go on her car...