Keep snapping the belt tensioner auxiliary fulcrum

When I'm taking off the tensioner shock absorber it's been ok, but putting it back on levering it into place caused one of the arms on the fulcrum to snap. I ordered a new one and levering it in position I snapped one of the arms again!

Now the tensioner shock looks to be now leaking a bit so I might replace it. Are there any other rips anyone has to performing this procedure of putting the shock on the fulcrum without snapping or putting undue stress on the arms?

Any help much appreciated.


Thanks

The belt tensioner? Petrol or diesel? My diesel has a hole in the front for a key to use to release it, might be half inch square, not sure.