We had that happen to our 450 when someone tried to retract the sliding floor with manure on it.  IIRC there is bushing that the cylinder goes into and the plate the bushing was welded into rotted off, the plate we fabricated to fix it was 1/2" thick and never had another problem.

Edit to add:
Pretty sure we had that happen on our 790 also, but I knew enough to not try to retract any further and did not damage the lines.