Towball?

caravan I purchased last year has an alko arrester and when collected from dealer the Alko arrester was in position with arm down level where it should be on hitching up. Now can get the arm down so hard I thought 'Stand on it' but change my minde hence the question.

Towball is 50mm and the extended neck is approx 15mm the unit locks on to the ball but cannot push down the alko arrester lever flat as it should be, it gets too hard to push down cosequently not acting as is should.

When hitched No problem hitch locks on but arrester arm won't go fully down and very hard to the point I thought of standing on it to lock it down.
In desperation am now looking to change the pads searching 'How to' Wondering if some clown packed the pads out instead of replacing worn pads.
many thanks