Does the block seem to 'wedge' and jam when pulled back?? Maybe you will have to remove the stoker assembly from the stove. Remove the hopper and lift the block out the top instead of sliding it out the back.
It is possible that the two side 'guides' that the block runs between taper to a too narrow gap near the back of the block's travel. This could be caused by a slight manufacturing error, or by rust on the metal, or paint too thick on the guides....?
This is the only thing I can think of.
By the way, welcome to the forum!!
Winter is back for a visit, 1/09/07, 20* at 7:00 AM but supposed to be 44* on Friday.