In all probability, the pump drive cam is causing some difficulty.

Wiggle the unit side to side and slightly up and down as you attempt to move the unit rearward. Be aware the unit may release suddenly so palce your body such that you do not get hit in the face as it releases if you haev the auto on jack stands. If on a lift, put the flange back snug and tie a rope or strap around it short enough to keep the unit from hitting the floor.

If a helper is around, turn the output shaft as you apply rearward pressure. This moves the cam and pump and allows any "jamming" to release as the unit moves.

If that fails, have the helper bang on the side of the rear case with a piece of wood as you apply rearward pressure. This also may cause a very suddden release so be ready.

Also any combination of the above may help to move the unit rearward.

Prying...a LAST resort...like after two hours or so of variations and combinations of the above. MUST be done with a wide pressure application device, NO SCREWDRIVERS, and whatever must be paired and opposite with pressure only at the stud bosses of the front case. Remove the studs to allow the Wonder Bars maximum contact. This method will POP the OD off for lack of a better word, instantly, so be ready.

Duane