Mounfield 5R rotovator

Can anyone help?  Having used the Mountfield 5R Rotovator on our plot it dug in rather than moving forward, our soil is very light loam but our old rotovator worked fine.  This machine looks to have the drag bar missing from the rear, does anyone know where I could get such a bar and do you think this is the problem.  As you may have guessed the said rotovator was purchased second hand in good allotment tradition.  Any ideas would be appreciated